Line bottom of an 8x12 inch baking dish with 1 layer of bread (about 1/2); trim to fit and reserve scraps. Top bread with 1/2 the mushrooms, onions, chilies, and cheddar; repeat layers, starting with bread and scraps and ending with cheese. Beat eggs and whites to blend with milk, mustard, and hot pepper seasoning; pour over mixture in casserole. Cover; chill at least 8 or up to 24 hours. Uncover and scatter chips over casserole. Bake in a 350° oven until golden, about 55 minutes; let stand for 15 minutes. Spoon out portions and season to taste with salt and salsa. Makes 8 to 10 servings. Per serving: 319 cal. (48 percent from fat); 18 g protein; 17 g fat (8.5 g sat.); 25 g carbo.; 667 mg sodium; 123 mg chol. BRUNCH26