n a large skillet on high heat add in the oil and garlic and sauté until golden, about 1-2 minutes. Lower to a medium heat, add in the sliced onion and sauté for 2 minutes, mixing occasionally.
Next, add in the zucchini, salt, and pepper, and sauté for 5 minutes, mixing occasionally.
Continuing on medium heat, add in the diced tomatoes and sauté until the zucchini is tender (about 5-8 minutes), mixing occasionally.
While you continue to cook make sure you are mixing occasionally to mix all ingredients and to ensure the zucchini is cooking evenly.