Preheat the grill on high. Remove the dirt, stems and gills from the mushrooms and set aside.
Form the Italian sausage into four patties. Place the pepperoni and mozzarella on a small plate.
Place the cherry tomatoes and sea salt into the blender and blend until chunky.
Lower the heat to medium and place the mushrooms cap side down. Spoon about ľ cup of sauce into each mushroom. Place the sausage patties on the grill and cook both sausage and mushrooms for about 8 minutes.
Turn the sausage patties over and layer five pieces of pepperoni and two slices mozzarella on each patty. Cook for 5-8 minutes until burgers are cooked through and cheese is melty.
Remove the mushrooms from the grill onto a serving plate. Stack the burgers on top of the mushrooms and garnish with fresh basil. Serve immediately with additional sauce.