Using a sharp, thin knife, cut a parallel slit in the side of each chicken breast, forming a pocket, taking care not to cut through top or bottom of chicken. (Or, ask your meat retailer to do this for you at time of purchase.)
Combine 1 cup cheese, pimientos and cilantro; stuff into pockets of chicken. Place chicken on a foil-lined baking sheet. Combine chili powder, cumin and garlic salt; rub mixture over both sides of chicken. Coat chicken lightly with cooking spray or brush with canola oil.
Bake in a preheated 400°F oven 20 minutes or until chicken is cooked through. Sprinkle remaining cheese over chicken. Continue baking 2 to 3 minutes or until cheese has melted.