Spread the chopped onion and mushrooms evenly in the bottom of a 9x13 inch baking dish. Arrange chicken pieces over the vegetables, skin side up. Squeeze lemon juice over the chicken pieces, and season with garlic salt and pepper.
Bake chicken uncovered for 20 minutes in the preheated oven. Carefully turn the pieces over, and continue cooking 15 minutes more.
Set oven to broil. Cook chicken for 5 minutes, or until chicken skin is crisp.
