Trim ends from zucchini and half each length-wise. Scoop out flesh of zucchini; dice. Arrange zucchini shells into a baking dish.
Heat olive oil in a 10-inch skillet over medium heat. Cook and stir onion, mushrooms, and garlic in hot oil until the onion is tender, 5 to 7 minutes; season with salt and pepper.
Stir diced zucchini flesh into the onion mixture; cook and stir until hot, about 5 minutes. Spoon zucchini mixture into the shells in the baking dish; top each with 1 tablespoon each feta cheese and Parmesan cheese.
Bake in preheated oven until the zucchini shells are soft, 30 to 40 minutes.
Tips & Tricks
Stuffed Butternut Squash
Baked squash are stuffed with Brussels sprouts, carrots, beans, and rice.
Connie's Zucchini "Crab" Cakes
Discover the secret that makes these crabless cakes taste like the real deal.