Layer cauliflower, pimento, green pepper, water chestnuts, eggs, onion and cheese in 2 1/2 quart casserole. Make sauce by melting butter and stirring in flour, salt and pepper. Cook and stir 1 minute. Add milk gradually. Add cheese and cook until thickened. Pour over vegetables. Combine topping ingredients; sprinkle over all. Bake at 350 for 30 minutes. Yield 12 servings.