Heat the Pan: Heat olive oil and butter in a large skillet over medium heat until the butter is melted and foamy.

Cook the Onions: Add the chopped yellow onion and sauté for 3-4 minutes until softened and slightly translucent.

Add the Mushrooms: Stir in the quartered mushrooms and cook for 5-6 minutes until they release their moisture and begin to brown.

Cook the Zucchini: Add the zucchini chunks to the skillet. Cook for 5-7 minutes, stirring occasionally, until the zucchini is tender but still slightly crisp.

Flavor the Dish: Stir in the minced garlic, Italian seasoning, red pepper flakes, and a pinch of salt and pepper. Cook for another 1-2 minutes, allowing the garlic to become fragrant.

Taste and Adjust: Taste the dish and adjust the seasoning with more salt, pepper, or red pepper flakes if desired.

Serve and Enjoy: Remove from heat and serve warm as a side dish to grilled chicken, steak, or fish, or enjoy as a light vegetarian main course.