Preheat oven to 400˚F.
Prepare the mushrooms by gently popping off the stems. Then, using a spoon, remove the brown gills from inside the cap. Wash the mushroom caps and pat dry with paper towels. Set aside.
Melt butter in a small bowl and whisk in parsley, garlic, 1/4 teaspoon salt, and 1/4 teaspoon pepper.
Brush the garlic butter mixture all over the mushrooms.
Transfer mushrooms to a rimmed baking sheet and bake for 8 to 10 minutes, or until softened.
Remove mushrooms from oven; arrange previously prepared cheese balls and tomatoes inside each mushroom cap. Place the cheese and tomatoes close together. You can always add more, or use less, tomatoes and cheese.
Season with remaining salt and pepper.
Bake for 12 to 14 minutes, or until cheese is completely melted.
Remove from oven.
Top mushrooms with fresh basil and drizzle with balsamic glaze.