1. Steam fresh cauliflower florets about 5 to 7 minutes or frozen florets according to package directions, just until crisp tender; drain.
2. Coat a saucepan with cooking spray. Saute green onions, celery and bell pepper until limp. Add seasonings. Blend in flour and cook 1 minute. Gradually add milk, stirring constantly. Simmer until mixture thickens. Remove from heat. Add cheese and stir until melted.
3. In a 2-quart baking dish, layer half the cauliflower, sliced tomatoes and water chestnuts. Pour half the sauce over. Repeat layers ending with sauce. Sprinkle with bread crumbs and parsley. Bake at 350 degrees F. for 24 to 30 minutes until bubbly and top is a light golden brown.