In a large skillet, heat over medium heat. Add the ground beef, diced onion, and minced garlic. Cook for 5-7 minutes until beef is browned and onions are translucent. Drain excess fat.
Stir in chili powder, cumin, salt, and black pepper. Cook for an additional 2 minutes. Remove from heat and mix in shredded cheddar cheese and refried beans.
Warm flour tortillas in the microwave for 30 seconds. Lay a tortilla flat, spoon about 1/3 cup of the beef and cheese mixture into the center, fold sides over filling, and roll tightly.
In a large skillet, heat about 1 inch of vegetable oil over medium-high heat. Add chimichangas seam side down and fry for 3-4 minutes on each side until golden brown and crispy.
Remove chimichangas from oil and place on a paper towel-lined plate to drain excess oil. Serve immediately.