Combine Chicken, water, Italian seasoning, pepper and bouillon cubes in a large pot. Cook on high for 45 min. Remove chicken to cool and shred. Continue to cook the liquid until ready to add with the chicken.
Cook pasta according to directions on package until al dente. Drain and set aside.
Clean and slice celery and leeks. Mince garlic.
In a lg skillet melt the butter on Med-High. Saute leeks, celery and garlic until soft (a little color wouldn't hurt). Sprinkle with flour and saute for about 3 min. stirring constantly.
Add 2 cups of the reduced liquid, the shredded chicken and stewed tomatoes (crushed) to pan. Simmer on Med-High for about 20 min, stirring occasionaly. Taste and add salt and pepper, if needed.
Spread cooked pasta in the bottom of a 9x13 baking dish. Cover with the chicken mixture evenly.
Combine the breadcrumbs and shredded cheese and sprinkle over the top of the chicken mixture.
Bake for 45 min, or until bubbly and golden brown.