Cook and stir the garlic, oregano, salt, pepper, and olive oil in a large skillet over medium heat until fragrant, 1 minute. Add the potatoes, mushrooms, and zucchini. Cover the skillet and cook the vegetables over high heat for 5 minutes. Stir, replace the lid, and reduce the heat to medium. Cook, stirring occasionally, until the potatoes are tender, about 15 minutes.
