In a large skillet over medium heat, cook ground beef, breaking it apart with a spatula. Add diced onion, cook until translucent, and season with garlic powder, cumin, chili powder, salt, and pepper. Mix well and remove from heat.
Lay out tortillas on a clean surface. Distribute beef mixture on each, add cheddar and Monterey Jack cheese. Fold sides inwards and roll tightly to form a burrito.
In a frying pan, heat oil over medium-high. Fry chimichangas seam-side down until golden on both sides. Transfer to paper towel-lined plate to drain excess oil.
Notes
Leftovers can be stored in the fridge for up to 3 days. Reheat in a preheated oven to restore crispiness.