Portobello, Mozzarella, and Fresh Basil Panini | America's Test Kitchen

Ingredients

• 1/2 cup mayonnaise
• 1/2 cup finely chopped fresh basil
• 1 tablespoon lemon juice
• 4 large portobello mushroom caps , gills removed, halved lengthwise
• 6 tablespoons extra virgin olive oil
• Salt and pepper
• 1 large red onion , halved and sliced 1/2 inch thick
• 2 red bell peppers , seeded, halved, and sliced 1/2 inch thick
• 8 slices thick-cut crusty bread
• 3/4 pound thinly sliced deli mozzarella