The Best Grilled Portobello Mushroom Burger
Balsamic-marinated portobello caps grilled until tender, topped with melted Swiss, grilled onion, tomato, spinach, and avocado on a toasted bun.
- 4 portobello mushroom caps
- 2 tablespoons balsamic vinegar
- 1 tablespoon low sodium soy sauce
- 1 tablespoon olive oil
- 1 tablespoon chopped rosemary
- 1-1/2 teaspoons steak seasoning, like Montreal Steak Grill Mates
- 4 thick slices red onion
- 4 oz reduced fat Swiss cheese, sliced thin
- 4 thin slices tomato
- 1/2 avocado, sliced thin
- Baby spinach
- 4 whole wheat low-calorie buns
- In a large bowl, whisk together the balsamic vinegar, soy sauce, olive oil, rosemary, and steak seasoning until combined.
- Place the mushroom caps in the bowl and toss with the marinade, using a spoon to coat them evenly. Let stand at room temperature for 20 to 30 minutes, turning a few times so both sides absorb flavor.
- Heat a grill or indoor grill pan over medium heat. Once hot, brush the grate with oil or lightly spray the grill pan to prevent sticking.
- Place the mushrooms on the grill, reserving the leftover marinade for basting. Grill for 5 to 7 minutes on each side, or until tender, brushing with the reserved marinade frequently as they cook.
- Top the mushrooms with the Swiss cheese during the last minute of cooking so it melts just before they come off the grill.
- While the mushrooms cook, grill the onion slices for about 1 minute on each side and toast the buns on the grill until lightly golden.
- To finish, layer the spinach and grilled portobello mushrooms onto the toasted buns, then top with the grilled onions, sliced tomato, and avocado.
Chef's Note: Marinating the portobello caps does more than season them — it also helps break down some of their fibrous texture, so the finished burger has a meatier bite than a plain grilled mushroom would. Basting frequently with the reserved marinade while grilling keeps the caps from drying out, since mushrooms lose a fair amount of moisture on direct heat.
Grilling the onions and toasting the buns alongside the mushrooms, rather than as a separate step afterward, is what keeps this recipe efficient despite having several components — everything finishes around the same time. This burger is best assembled and eaten right away while the cheese is still melted and the mushrooms are hot off the grill.
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