Double-Decker Marinated Portobello "Burger"

Ingredients

• 0.3 cup balsamic vinegar 
• 0.5 teaspoon pepper black freshly ground plus more for seasoning
• 1 loaf ciabatta bread 
• 2 medium garlic clove finely chopped
• 1 teaspoon kosher salt plus more for seasoning
• 0.5 cup olive oil 
• 3 pounds portabello mushrooms dark
• 10 ounces provolone cheese thinly sliced
• 2 tablespoons red wine vinegar 
• 4  the of 1 cos lettuce 
• 0.3 inch tomato ripe (from 2 medium, tomatoes)

Equipment

• bowl
• baking sheet
• knife
• whisk
• grill
• grill pan
• cutting board

Directions

1. Place the vinegars, garlic, measured salt, and measured pepper in a medium, nonreactive bowl. While whisking continuously, add the oil in a slow, steady stream until evenly incorporated.
2. Place the mushrooms cap-side down in a single layer on a baking sheet and pour the marinade over them. Turn several times to coat, and let sit at room temperature for 30 minutes.
3. Heat a grill pan or outdoor grill to high (about 450°F to 550°F). Slice the ciabatta widthwise into 4 pieces, each slightly smaller than the width of the mushrooms (you may have some bread leftover). Slice each piece in half horizontally to make 4 tops and 4 bottoms.
4. Place the halves cut-side down on the grill and cook until brown and toasted, about 2 to 3 minutes.
5. Remove the bread to a cutting board or work surface.
6. Spread 1 heaping teaspoon of the pesto on each ciabatta top and bottom (2 teaspoons per sandwich—you’ll probably have some pesto leftover).
7. Place 2 tomato slices on each bottom and season with salt and pepper. Set aside while you grill the mushrooms.
8. Place the mushrooms cap-side up on the grill, close the grill, and cook until just starting to become tender, about 4 minutes. Flip the mushrooms, top each with a quarter of the cheese, close the grill, and continue cooking until the mushrooms just give way when pierced with a knife and the cheese is melted, about 4 minutes more.
9. Remove the mushrooms from the grill. Stack 2 mushrooms on top of each other, cheese side up, and place on a bottom piece of bread. Repeat with the remaining mushrooms and bread bottoms. Top with the lettuce leaves and bread tops and serve immediately.