In a large mixing bowl, combine the shredded chicken, salsa, shredded cheddar cheese, shredded Monterey Jack cheese, diced green chilies, ground cumin, chili powder, garlic powder, onion powder, and salt. Mix well until all ingredients are evenly distributed.
Place a generous scoop of the chicken mixture in the center of each flour tortilla.
Fold the sides of the tortilla over the filling, then roll it up tightly from the bottom to create a sealed burrito shape.
Place the chimichangas seam-side down on a baking sheet.
Brush the tops with melted butter.
Bake in the preheated oven for 20-25 minutes, or until the tortillas are golden brown and crispy.
Remove from oven and let cool for a few minutes before serving.
Serve with optional toppings such as sour cream, guacamole, additional salsa, and chopped cilantro.