Sauteed Zucchini with Onion and Garlic. Place the sliced zucchini or summer squash into a colander, place the colander into a large bowl. Sprinkle zucchini with a good dash of salt. Place a small serving plate on top and press down firmly. Set aside for at least 2 hours. Place a heavy duty skillet onto a burner , heat the skillet up, butter into the hot pan followed by the squash, onion, garlic, salt and pepper. Saute until onion is caramelized to a golden brown. Stirring often.