PREPARATION:

1. Preheat broiler. Heat oil in large skillet over medium-high heat until hot. Add broccoli, mushrooms and onions. Cook and stir 3 minutes or until crisp-tender; set aside.
2. Place English muffin halves on baking sheet. Broil 1 to 2 minutes or until light golden brown. Remove from oven and spread each half with 2 teaspoons mustard. Top with vegetable mixture. Sprinkle each with about 2 tablespoons cheese. Broil 1 to 2 minutes more or until cheese is melted. Serve immediately.