Preheat oven to 400f.
Combine the oil, garlic and 3 tsp. Italian seasoning together in a small bowl.
Brush the bottoms of each mushroom with the garlic/oil mixture and place each mushroom, oil side down, on a lightly greased baking sheet / tray.
Fill each mushroom equally with mozzarella cheese and top with tomato slices.
Broil in preheated oven until cheese has melted and is golden in color (about 8 minutes).
To serve, sprinkle with the remaining Italian seasoning (or mixed fresh chopped herbs), and season with sea salt and pepper to taste.