Step 1Cut the ends off the zucchini. If the zucchini are small in diameter, leave them whole. If large, cut them in half lengthwise. Slice the zucchini paper-thin, using the slicing blade of a grater or a mandoline.
Step 2Mash the garlic in the salt until dissolved to a paste.
Step 3Heat the butter and oil in a large nonstick skillet over medium heat.Add the garlic and onion and cook until the onion is tender, 5 minutes. Add the zucchini slices and cook until tender, stirring as needed to cook evenly, 6 to 8 minutes. Sprinkle with pepper, if desired.