In a large skillet, heat over medium heat, adding the ground beef and finely diced onion. Cook for about 5-7 minutes, stirring occasionally until the beef is browned and the onion is translucent. Drain any excess grease from the skillet. Add minced garlic, taco seasoning, and salsa, mixing well. Let the mixture simmer for another 2-3 minutes until heated through and aromatic.

On a clean surface, warm each flour tortilla to make them pliable. Begin by spreading a spoonful of refried beans (if using) in the center of the tortilla, followed by a generous scoop of the beef mixture and a handful of shredded cheese. Carefully fold in the sides of the tortilla and roll it tightly from the bottom to encase the filling securely, ensuring no gaps are left.

For frying, heat vegetable oil in a deep pan over medium-high heat until it reaches 350°F (175°C). Place the chimichangas seam-side down into the hot oil, frying them for 2-3 minutes until golden brown and crisp on the outside. Using tongs, carefully remove them and let them drain on paper towels. For baking, preheat your oven to 400°F (200°C), brush the chimichangas with oil, and arrange them seam-side down on a baking sheet. Bake for 20-25 minutes until they are crispy and golden.

Allow the chimichangas to cool slightly on a wire rack before serving. These crispy Beef and Cheese Chimichangas can be garnished with fresh cilantro or chopped green onions for an added burst of flavor. Serve them alongside your favorite dipping sauces like sour cream or guacamole.