This warm, cheesy sandwich will make your taste buds water.
- Toast muffin halves and place on a baking sheet in a single layer.
- In a large skillet over medium-high heat, sauté onions and mushrooms in oil, stirring often, until just beginning to brown.
- Add asparagus, seasoning and vinegar. Sauté, stirring often, until asparagus is barely tender. Season lightly with salt and pepper.
- Divide the vegetable mixture equally onto the muffin halves. Top each muffin with shredded cheese.
- Broil muffins until the cheese melts. Watch carefully to avoid burning.
- Refrigerate leftovers within 2 hours.