6 portobello mushrooms
1 large red onion
¼ cup olive oil
2 tablespoons lime juice
2 tablespoons soy sauce
½ teaspoon red pepper flakes
1 large tomato
1 cup baby spinach leaves
6 slices pepper jack
6 potato rolls
Miller Lite Whole-Grain Mustard, for serving
Mayonnaise, for serving
1. Remove the stems from the mushrooms and wipe the caps clean. Peel and slice across the onion to cut it into rings, about ½-inch each; try to keep the layers together.
2. Combine the olive oil, lime juice, soy sauce, and red pepper flakes in a bowl and brush it all over the mushrooms and onions. Set aside. Separately, cut the tomato into six slices.
3. Prepare your grill with medium-high heat, leaving an area for indirect heat and let it get warm for at least 5 minutes. Add the onions first and give them a minute or two to start cooking and softening before you add the mushroom caps, stem side up. Cover the grill and cook for about 4 minutes, until the mushrooms have nice grill marks, then flip the mushrooms and onions. Cover and cook for another 2 to 3 minutes.
4. Flip the mushrooms upside-down again and fill each one with a slice of tomato and a handful of baby spinach. Top with a slice of cheese and move to indirect heat. Meanwhile, split the rolls and toast them over the high flame for 20 to 30 seconds until warm.
5. To serve the burgers, spread mayonnaise and Miller Lite Whole-Grain Mustard over the rolls, then add the mushrooms and grilled onion.