Place chicken in a large pot, water to cover, salt, peppercorns, celery & bay leaf. Bring to a boil, lower the heat and simmer gently, skimming as necessary, until chicken is tender (30-40 minutes). Let chicken cool in broth. Remove the meat from the bones & strain the broth.
Place 1 1/2 C. broth into saucepan, boil. Combine cornmeal with 1/2 C. of the remaining broth; stir into boiling broth, cover & cook 10-15 minutes until mixture thickens.
Preheat oven to 350 degrees. Cool the mush slightly and use to line the bottom and sides of a 2 1/2 quart casserole.
Melt butter; cook onions & garlic in butter till transparent. Add tomatoes and seasonings & simmer 15 minutes. Add corn & salt to taste.
Spread chicken over the center of the mush-lined casserole and cover with the tomato, corn mixture. Sprinkle with cheese and bake 30 minutes.