Mix white wine vinegar with balsamic vinegar, sugar, salt and pepper until the sugar has dissolved. Beat the oil under it. Add the onions and basil to the sauce, mix well and pour everything together over the quartered tomatoes.
Wash the avocado, cut in half, remove the stone, peel and cut the flesh into small pieces. So that the avocado does not turn brown, drizzle with the lime juice immediately. Mix carefully into the salad.
It looks very nice when the salad is served in the avocado bowls.