The POD for this requires something completely different from otl' Europe of the Early 19th Century. After the Napoleonic Wars, the Coalition allies signed a pact that they would keep the peace as a commitment to keeping the balance of power for 20 Years. Russia and Austria took this seriously, as they avoided striking at the Ottomans when they were badly weakened. The Egyptian revolt would have been one such opportunity for this.
And as others have already pointed out, most of the initial Balkan revolts were over the issues of taxation and autonomy. Greece after it attained its independence was a very poor state. Greece, especially without Thrace and Makedonia is in a dire economic position. Bulgaria had much of the industrial resources in the Balkans. Plus the Eastern Roman Empire derived its wealth from the Black Sea trade and its holding in Anatolia where much of its wealth and manpower was. Greece also after its independence, was heavily saddled with massive amounts of debt that essentially crippled it.
Greece realizing its irridentist claims requires a POD that stems from something completely different from otl's Europe and Greek Revolution. It would likely have to be accomplished through a successful Napoleonic France (First Empire not the Second Empire) for this to work. Though this requires Napoleon to restrain his ambition, which he had shown he was capable of doing. Napoleon after all initially wasn't a champion of Polish independence, and sought to forge an alliance with Tsar Alexander. The two had a bit of camaraderie going at Tilsit, leading many to speculate that Britain's worst nightmare, a Franco-Russian Alliance was about to be solidified. This almost happened in otl, but Talleyrand started sabotaging Napoleon. Supposing Napoleon does manage to arrange for this more concrete Franco-Russian alliance he'd likely have to take Russia's interests into mind. Austria here would be in a panic as its now sandwiched between Napoleonic France and the Russian Empire. Though if Tsar Alexander with his mother's influence declines Napoleon's attempts marry Grand Duchess Olga, the Tsar's sister, the Habsburgs could very well try to save themselves like in otl by arranging a marriage between Napoleon and Marie Louise. This would be a Prussia screw most likely, as Prussia would likely be forced to cede Silesia to Austria. Napoleon here would also would likely keep Austria around as a willing economic and military partner perhaps as a counterbalance to Russia.
If Napoleon doesn't embark on his Penninsular Campaign, he could very well work with Russia, Austria, and Prussia to Partition the Balkans. Through this way Greater Greece could be realized. Austria likely gains dominion over the Western Balkans restoring Croatia's historic boundaries while also vassalizing Serbia as a new Kingdom centered in Belgrade. They have historic claims to the regions, as they had once captured it in the 18th century wars against the Ottomans. I could see Bulgaria being restored and placed under the Russian Sphere. Wallachia though would likley be an Austrian vassal while Molodovia would be likely annexed by Russia. Greece here could emerge with France and Russia supporting it.
The Ottomans almost could have collapsed in the early 1800's as the Jannisaries in a revolt, and palace coup, nearly wiped out the Ottoman Royal House of Osmangolu leaving it with only one man (Sultan Mahmoud). If Mahmoud is killed off, this could very well spark a massive civil war. Though the Girays might try to take the throne as they are closely related to the Ottomans. The French, Austrians, and Russians could pounce on the Ottomans in its weakness with the situation mirroring the Partition of Poland following the Deluge. This way, Tsar Alexander dusts off his grandmother
Catherine the Great's plan of restoring the Byzantine Empire. She had after all intended for her other Grandson, Grand Duke Constantine to take its throne. Though France and Austira would want the crowns to be separate like the Crowns of Italy and the French Empire proper. Thus Kingdom would be in a personal union with Russia with a new Romanov Basileus at its helm. Thus the new Third Rome actually realizes its claim by retaking Constantinople. Through the Caucuses, Russia could likely partition the Ottoman Empire setting up client states in the Caucuses. Trebizond and Pontus along with the other Western Portions of Anatolia would go to this new Byzantine Empire with a Turkish rump state being kept in the interior.
Napoleon likely seizes and vasssalizes North Africa and the levant as well. Thus a new European order in Europe would be created. The new Caesar Napoleon would rule the West, while the Austria rules the Danube, and the new Eastern Basileus rules in Constantinople which has been retaken into the hands of Orthodox Christianity.
Britain will likely have a panic over this and would likely try to support the Ottomans to prevent such a massive alliance from threatening it.
