For the vinaigrette, whisk vinegar, salt, pepper and honey. Add oil drop by drop to the vinaigrette. Peel onion and cut into fine slices. Wash the basil, shake dry and cut into strips, except for a little to garnish.
Stir basil and onion into the vinaigrette. Wash, clean and slice the tomato. Marinate tomato slices with vinaigrette and arrange on a plate. Garnish with basil.