Heat a 10-12 inch skillet over medium heat. Add the butter or oil and allow to just melt.
Add the zucchini, mushrooms, and onions to the hot pan and arrange in an even layer. Allow the vegetables to cook for about 3 minutes before stirring. Stir every couple of minutes for about 6-8 minutes until tender.
Add the garlic, salt, and pepper and stir for another 30-60 seconds or until the garlic is fragrant.
Notes
Serve hot as a side dish or over rice or pasta for a light meal.