Little Donkey County (16th Century - 18th Century)
(In this ATL, Britain and France colonised central/south america while Spain and Portugal colonised the north.)
Little Donkey County started as a small Scottish colony in OTL Tamaulipas around the 1500's, consisting of a few thousand peasants looking for a new life. The protestant reformation lead the British Empire to boot many Catholics out of the mainland, which led to several English and Celtic catholic immigrants making their way to the colony of Belize forming additional settlements.
With the coming of the decline of colonialism around Europe, Central America was scattered. While the Spanish already completely took over Florida, Texas and California beforehand, much of Mexico was still in the hands of The Aztecs and other native nations. Naturally, they were all slaughtered and assimilated into the English speaking colonies. Native culture came to be romanticised later on, though, as the small nations in Mexico wanted to distinguish themselves from the British Empire. Thus, the Belizeans drew their culture heavily from the natives once they weren't deemed "savages" any more.
The colony of Tamaulipas in OTL would come to be known as Little Donkey County (Literal translation of Burrito), which prided itself on its agriculture and culinary artists. Italian emigration was also common here in this time period, so Belizean cuisine became a mix of Italian, Spanish and British.
The unusual tricolour in the center of the flag is a nod to Italy's flag, but the colours instead are brown for the nutrient-rich mud of the county, green for the jungles down south and the plentiful crops, and red for the crimson sand of the Mexican deserts. The stars represent the languages of the colonists: Scottish, English, Irish, Welsh, Spanish and Italian, which became one in the melting pot of the county.
Eventually, all the colonies would be annexed by the Belizean Federation, which came to control and own all of OTL Mexico in the present day.
(I tried to make the diamond look like the meat, lettuce and tomatoes of a burrito, but I wanted to come up with something more "realistic" than that.)