Chop onion, celery and green peppers. Put in oven proof casserole dish. Season with salt and pepper. Place lemon slices on top of vegetables. Place chicken on top of lemons. Melt butter and pour over all ingredients and bake in a preheated 350 degree oven for 30 minutes. Turn chicken and cook for another 30 minutes.
Remove from oven and place chicken on a serving platter.
Pour chicken stock in a pan and add contents from baking dish to stock. Bring to a boil and thicken with cornstarch slurry. Pour over chicken and serve over noodles or rice.