On baking sheet drizzle some olive oil and then brush the mushrooms caps with the oil as well and line them up in rows. Preheat oven to 350 degrees.
Grate the zucchini and then place it in a paper towel and squeeze out all the excess water and then place the dry zucchini in the mixing bowl.
Next, add to the zucchini the parmesan cheese, basil, bread crumbs, onion, garlic and some salt and pepper and mix well to combine.
Last, add 2 cubes of the mozzarella to each mushroom cap and then fill each one with the zucchini mixture. Then take the rest of the mozzarella cubes and add them to the top of each cap and bake for 20-25 minutes until done.
I top each stuffed mushroom with some more basil for garnish and serve! :)