Preheat oven to 375° F. Cut squash in half lengthwise. Scoop out pulp with a teaspoon, making a ¼ inch thick shell to hold the stuffing. Coarsely chop pulp and set aside.
In a skillet, heat oil over medium heat. Add onion and cook for 3 minutes. Add garlic and cook for an additional minute.
Add squash pulp and mushrooms. Cook for 2 to 3 minutes until the pulp is tender, stirring frequently. Remove from heat.
Stir in tomato, breadcrumbs, herbs, salt, and pepper.
Spoon mixture into zucchini shells. Arrange zucchini in a baking dish and cover with foil. Bake for 20 minutes.
Remove foil and sprinkle with parmesan cheese. Bake 15 to 20 minutes, until shells are tender. Let cool 5 minutes before serving.