Portabella, Pesto Focaccia Sandwich

Ingridients of Portabella, Pesto Focaccia Sandwich:

• 2 tablespoons olive oil
• 4 large portabella mushrooms , stem & gills removed
• 4 slices cheddar cheese , 1/4 inch slices, the cheese is to fit inside the mushroom caps
• 1 rosemary focaccia bread or 1 herb focaccia bread
• 1/4 cup pesto sauce, homemade or 1/4 cup store bought pesto sauce
• 4 slices tomatoes (thick slices)
• lettuce (to garnish)
• salt & pepper