A chimichanga is simply a burrito made with a flour tortilla which is folded then chilled to allow the edges to seal. The burrito is then fried until crisp. Fillings vary from vegetarian beans and rice, to chicken and beef. A typical version includes minced beef with potatoes and seasonings like chile powder and Mexican oregano.
The heritage is disputable and there seem to be many stories about the origins of this dish.
Many report the "chimichanga" dates back to the 1950's in Tucson Arizona.
Diana Kennedy explains in Cuisines of Mexico (1972) that fried burritos are a common food in Mexico and referred to as chivichangas.
The Food Lover's Handbook To The Southwest (1992) have a more colorful theory. The author explains the term changa means a female monkey and that the dish was born when a burro was knocked into a deep fat fryer. Further stories reported that a burrito made with baked burro was called a baked monkey and that the term chimichanga means toasted monkey.