Avocado Chicken

3-4 chicken breasts
Butter
1/2 c chopped onion
1 clove minced garlic
1 pkg sliced fresh mushrooms
2 T flour
1 t celery salt
White pepper
1/2 c chicken broth
1/2 c white grape juice (or additional broth)
2 avocados
1 1/2 c grated Monterey jack cheese

Cut chicken into 1/2s or pound thin.  Sprinkle both sides with salt, black pepper and flour.  Sauté in butter until browned but not cooked through.  Put in 9x13.  In same skillet, put 1/4 c (or less) butter.  Sauté onion, garlic, & mushrooms til soft.  Add 2 T flour and celery salt, white pepper, chicken broth and juice.  Thicken.  Stir in mashed avocados and 1/2 c cheese.  Pour over chicken and sprinkle 1 c cheese over.  Bake at 350 25 minutes (sauce bubbly).  Broil at end to crisp.  Serve over noodles.