Heat olive oil or butter in a large skillet over medium heat

Add sliced onions and sauté until slightly softened

Stir in the garlic and cook briefly until fragrant

Add mushrooms and cook until they release their moisture and start to brown

Add sliced zucchini to the skillet

Season with salt, pepper, and thyme or Italian seasoning

Cook while stirring occasionally until zucchini becomes tender but not mushy

Allow vegetables to lightly caramelize for extra flavor

Remove from heat and sprinkle with fresh parsley

Serve immediately while warm