In a large mixing bowl, combine the shredded chicken, salsa, chili powder, ground cumin, garlic powder, onion powder, red pepper flakes, salt, and pepper. Mix well until all the ingredients are evenly combined.

Add the Cheddar and Monterey Jack cheese to the chicken mixture and stir until the cheese is uniformly distributed.

Place a tortilla on a flat surface and spoon approximately 1/3 cup of the chicken mixture into the center.

Fold the sides of the tortilla over the filling and roll it from the bottom up, ensuring the filling is enclosed. Secure with a toothpick if necessary.

Repeat this process for the remaining tortillas and filling.

In a deep skillet, heat about 2 inches of vegetable oil over medium heat until it reaches around 350°F (175°C).

Carefully place the chimichangas seam-side down in the hot oil, frying 2-3 at a time to avoid crowding.

Fry the chimichangas for 3-5 minutes on each side, or until they are golden brown and crispy.

Use a slotted spoon to remove the chimichangas and let them drain on paper towels to remove excess oil.

Serve the chimichangas hot, topped with sour cream, guacamole, and a sprinkle of chopped fresh cilantro for garnish.