In a large skillet over medium heat, brown the ground beef and diced onion until meat is no longer pink, about 5-7 minutes. Drain excess grease, add garlic, taco seasoning, and salsa. Simmer for 2-3 minutes.

Lay out the tortillas on a clean surface and spread a layer of refried beans (if using) over each. Spoon beef mixture onto the center of each tortilla, sprinkle with shredded cheese, fold in sides, and roll tightly from the bottom up.

For frying, heat oil to 350°F (175°C) and fry chimichangas seam-side down for 2-3 minutes on each side until golden. For baking, preheat oven to 400°F (200°C), brush with oil, and bake for 20-25 minutes.

Let chimichangas rest for a few minutes before serving. Top with sour cream, guacamole, or fresh salsa as desired.