Ingredients:
- 4 portobello mushroom caps
- 2 Tbsp. balsamic vinegar
- 1 Tbsp. soy sauce
- 1 Tbsp. olive oil
- 1 Tbsp. chopped rosemary
- 1 1/2 tsp. steak seasoning
- 4 slices red onion
- 4 slices Swiss cheese
- 4 thin slices tomato
- baby spinach
- 4 buns, toasted
Directions:
- In a large bowl, whisk together vinegar, soy sauce, olive oil, rosemary and steak seasoning.
- Place the mushroom caps in the bowl and toss with sauce, using a spoon to evenly coat. Let stand at room temperature for 30 minutes to an hour, turning a few times.
- Heat the skillet over medium heat. When hot, brush the pan with oil or lightly spray.
- Place the mushrooms in the pan, reserving marinade for basting. Cook for 5 to 7 minutes on each side, or until tender, brushing with marinade frequently.
- Top the mushrooms with cheese during the last minute of cooking. While the mushrooms cook, cook the onions for about 1 minute on each side.
- To finish, place the spinach and grilled portobello mushrooms on the buns and top with the onions and sliced tomato.
