Chinese goes expansionist in Medival age (Zeng He discovered the African coast OTL. Emperor does not destroy the junk fleet for ideological reasons. Maybe you can get Chinese Mandarin administered provinces on the East African coast.
This is honestly a very bad idea of how the treasure fleet worked.
There were Chinese traders in East Africa since at least Tang times. Al-Idrisi in 1065 mentions how one East African island became a major trade hub, for example:
Opposite the coasts of Zanj [East Africa] are the Zalej Islands [...] It is said once that when Chinese affairs were troubled with rebellions, and when tyranny and confusion became intolerable in India, the Chinese moved their commercial center to Zalej [...] This is why the island is so populous and so frequented by strangers.
In one Swahili site alone, 1656 shards of porcelain were discovered. Many Swahili mosques or mansions have niches specifically designed to contain Chinese porcelain, and Song coins have been found throughout the Swahili Coast. This isn't because of the Zheng He treasure fleet, this is a natural result of centuries of private Chinese traders following the African coast down to the Atlantic (a Yuan map in 1312 accurately portrays the northward curve of South Africa). There's a reason the Swahili sultans first thought the Portuguese were Chinese; there was precedent for non-sewn ships with pale-skinned crews coming from the south.
So Zheng He did not discover Africa. In fact, every place Zheng He visited, from Malindi to Malacca and Jiddah to Java, had already been visited by the Chinese in a non-governmental manner, often for centuries. The treasure fleet only served to enforce the Chinese state's dominance in the Indian. And it was scrapped mainly because it achieved little compared to its price moreso than some Confucian reactionarism which is so often blamed.