Cook fresh asparagus spears in a small amount of boiling water for 8 to 10 minutes or until crisp-tender; drain. Reserve 3 spears for garnish; cut remaining asparagus into 1-inch pieces. Or, cook frozen asparagus according to package directions; drain. Set aside.
Meanwhile, in a medium mixing bowl beat eggs until foamy. Beat in cottage cheese, mustard, salt, and pepper; set aside.
Spray a 10-inch ovenproof skillet with nonstick spray coating. Cook mushrooms over medium heat until just tender. Stir in asparagus pieces. Pour egg mixture over mushrooms and asparagus. (If using fresh asparagus, arrange the 3 reserved spears on top.)
Cook mixture over low heat about 5 minutes or until mixture bubbles slightly and begins to set around the edges.
Bake frittata, uncovered, in a 400 degree F oven about 10 minutes or until set. Garnish each serving with tomato. Makes 4 servings.