Portobello Burgers with Pesto Mayo

Remove stems from mushroom caps and wipe caps clean with a clean damp kitchen towel. Place caps onto a large baking sheet with sides.

Combine all marinade ingredients in a jar with a tight-fitting lid. Screw the lid on tight and shake until mixture is thoroughly combined. Pour marinade over all prepared mushrooms on the baking sheet. Cover loosely with plastic wrap and let marinate for at least 30 minutes, turning every 10 minutes.

Stir pesto and mayonnaise in small bowl to blend; set aside.

Preheat grill or barbecue to medium-high heat.

Place mushrooms on the preheated grill, rounded side up for about 4 minutes. Turn mushrooms over. Cover and grill until mushrooms are tender, about 4 to 6 more minutes.

Place buns open face down onto the grill to warm and toast.

Place 1 slice of cheese on top of each mushroom and cover until melted. Serve immediately.

Slather each roll with pesto mayonnaise and place 1 mushroom on each roll bottom. Top each with lettuce, tomato and onion. Press roll tops over and serve.