Portabella, Avocado and Pepper Jack Sandwich

Ingredients

 * 24 (about 2 ounces each) portabella mushroom caps
 * olive oil, as needed
 * salt, as needed
 * coarsely ground black pepper,as needed
 * 2¼ cups mayonnaise
 * 7 tbsp lemon juice, divided
 * 8 California avocados
 * 24 round sandwich buns
 * 24 one-ounce slices pepper jack cheese
 * 24 lettuce leaves
 * 24 thin slices tomato

Directions

 * 1) Brush each portabella cap with oil; sprinkle well with salt and lightly with pepper.
 * 2) Arrange on a sheet pan.
 * 3) Mix mayonnaise with 3 tablespoons lemon juice and 1½ teaspoons pepper; reserve.
 * 4) Just before service, peel and roughly diced avocados with 4 tablespoons (¼ cup) lemon juice.

Per order

 * 1) Toast bun.
 * 2) Meanwhile heat 1 portabella cap on the grill or in a hot frying pan.
 * 3) When bun is ready.
 * 4) Spread ½ tablespoon seasoned mayonnaise on each cut side.
 * 5) Put portabella, stem side up on bottom of bun; fill cap with ⅓ cup diced avocado.
 * 6) Top avocado with 1 slice cheese.
 * 7) Heat in a hot oven until cheese begins to melt, about 2 minutes.
 * 8) Top with 1 lettuce leaf, 1 slice tomato, and top of bun.