For the salad: Divide the lettuce into leaves, rinse, spin dry and tear into small pieces. Trim and rinse the zucchini and cut into thin strips. Rinse the tomatoes, halve, cut out the stems and chop. Peel the onions and cut into thin rings. Rinse the peppers, halve, remove the seeds and ribs and chop. Peel the garlic and chop finely. Cut the feta cheese into cubes.
For the vinaigrette: Whisk the vinegar, salt and pepper, together in a small bowl. gradually drizzle in the olive oil and stir in the parsley and the garlic. Toss the vinaigrette with the remaining salad ingredients, arrange on plates and garnish with lemon balm. Serve with toasted bread.