Preheat your air fryer to 375°F (190°C) to ensure it's ready for immediate crisping.

In a large skillet over medium-high heat, brown the ground beef with the diced onion until the beef is fully cooked and the onion is soft. Drain any excess grease.

Stir in the taco seasoning, black beans, and cooked rice (if using). Cook for 2 more minutes until everything is heated through. Remove from heat and let it cool slightly.

Lay a flour tortilla flat. Spoon about 1/2 cup of the beef mixture into the center. Top with shredded cheese.

Fold in the left and right sides of the tortilla, then roll it up tightly from the bottom to the top to form a burrito shape.

Brush the outside of the burrito generously with melted butter. This is crucial for that golden-brown, crispy texture.

Place the chimichangas seam-side down in the air fryer basket. You may need to cook in batches depending on the size of your air fryer. Do not overcrowd.

Air fry at 375°F for 10-12 minutes, flipping halfway through, until they are golden brown and crispy on all sides.

Carefully remove from the air fryer and let them rest for 2 minutes before serving with sour cream, salsa, and lettuce.