- 2 tablespoons brown spicy mustard
- 3 tablespoons balsamic vinegar
- 1/2 cup olive oil
- 1 teaspoon kosher salt
- 1/2 teaspoon freshly ground black pepper
- 1 teaspoon hot sauce
- 4 portobello mushroom caps
- 4 slices Gouda cheese
- 1/2 cup mayonnaise
- 4 hamburger rolls
- 1 red onion, sliced
- 4 leaves butter lettuce
- 1 tomato, sliced
Combine marinade ingredients. Place caps into a baking dish and pour marinade over top. Use a brush to make sure all caps are covered with the marinade. Set aside and let marinate up to 2 hours.
Remove the portobellos from marinade (do not discard marinade) and place gill side down on a preheated gas, electric or charcoal grill over medium-high heat. Grill 3 to 4 minutes per side. Top each cap with cheese 2 minutes to melt before they are finished grilling.
In a medium bowl combine 1/2 cup mayonnaise and 2 tablespoons of the marinade.
Spread the flavored mayonnaise onto each bun and top with portobellos. Serve with sliced onion, lettuce and tomato.