Prepare the Chicken Filling: In a large mixing bowl, combine 2 cups shredded cooked chicken, 1 cup salsa, 1 cup shredded cheddar cheese, 1 cup shredded Monterey Jack cheese, 1 small finely chopped onion, 1 tsp ground cumin, 1 tsp chili powder, ½ tsp garlic powder, and ½ tsp paprika. Mix thoroughly until all ingredients are well incorporated. Taste your mixture and adjust the salt and pepper as needed.
Assemble the Chimichangas: Take one of the 8 large flour tortillas and lay it flat on a clean surface. Spoon approximately ½ cup of the chicken filling into the center of the tortilla. Fold the sides of the tortilla over the filling, then roll it tightly from the bottom to the top to create a burrito shape. Use toothpicks to secure the ends, preventing the fillings from spilling out during frying.
Fry the Chimichangas: In a deep skillet, heat 1 cup of vegetable oil over medium-high heat until it reaches a temperature of 350°F (175°C). Carefully place a few chimichangas into the oil at a time, ensuring not to overcrowd the pan. Fry each chimichanga for about 2-3 minutes on each side or until they are golden brown. Once done, remove them with a slotted spoon and drain on paper towels to remove excess oil.
Serve and Garnish: Once the chimichangas have cooled slightly, carefully remove the toothpicks. Serve them warm on a platter and top with your favorite garnishes such as sour cream, guacamole, diced tomatoes, shredded lettuce, salsa, or chopped cilantro.