Melt 1 tbl of the butter in the oil in a large heavy skillet over medium heat. Add the zucchini; cook, tossing constantly, until just wilted, about 3 minutes. Transfer to a large bowl. Add 1 Tbl butter to the skillet. Add the red pepper. Cook over medium-low heat until almost tender, about 5 minutes. Add this to the zucchini. Add the remaining 1 Tbl butter to the skillet. Add the onion; cook over medium-low heat for 1 minute. Add the garlic; cook 5 minutes. Add this to the zucchini mixture. Toss the tomato with the oregano in the skillet over medium-high heat for 1 minute. Add this to the zucchini mixture along with the parsley, sliced lemon, and vinegar. Let stand, covered, 1 hour. Add salt and pepper to taste before serving.