Clean mushrooms and remove stems.
Place on a non-stick sheet pan and brush each side of the mushroom with olive oil.
Sprinkle some salt and pepper on each side.
Place 2 tsps. of pesto sauce into each mushroom and brush evenly.
Fill each mushroom with 1/4 cup of shredded mozzarella cheese and then sprinkle some fresh basil on top of the cheese.
Add a few pieces of tomatoes, leaving spaces between them. Fill those spaces with the fresh shredded mozzarella cheese. Top with more chopped basil leaves.
Bake in a preheated 375 degree oven for 12 minutes then turn on the broiler to broil the top for 1-2 minutes until the cheese obtains a golden color.
Remove from heat and serve.