The chimichanga is a burrito that has been turned into a different sandwich by a single decision: it is deep-fried. A folded flour tortilla wrapped around a filling is a soft, pliable package; drop that package in hot oil and the tortilla stops being a wrapper and becomes a rigid, blistered, golden shell. That transformation is the whole identity. The chimichanga is not a burrito with a topping, it is a burrito whose container has been structurally re-engineered by the fryer into something closer to a pastry crust.
The craft is in the seal and the frying, because both have one job, which is not letting the thing burst. The tortilla is folded into a fully closed parcel with the seam tucked underneath, since any gap is where hot oil drives in and steam blows out. The filling, usually shredded beef or chicken with beans, is cooked and on the dry side before it goes in, because a wet filling generates steam that ruptures the seam and the bake time is set by the shell, not the center. Fried hot and fast, the tortilla crisps into an even, bubbled crust while the inside stays moist; fried slow or overfilled, the seam fails and the chimichanga unloads into the oil. Once it is out, the sandwich logic inverts: the shell is now the only hard, dry element, so it is crowned with the wet, cold counter a fried package lacks, a flood of cheese, sour cream, guacamole, or sauce that turns a handheld parcel into a knife-and-fork plate.
The variations stay inside the fried-shell frame. The plated build smothers it in red or green chile sauce and melted cheese until it is eaten with a fork; the handheld build keeps the toppings light enough to pick up; a sweet version fries a fruit or cream filling and dusts it with sugar, pushing the form toward dessert. Each of those is a codified reading with its own rules, and each deserves its own article rather than being crowded in here.