In a large bowl, combine the tomatoes, onions, mozzarella, and basil.
In a smaller bowl, whisk together the olive oil, vinegar, honey, optional garlic, optional mustard, salt & pepper. Or put all in a small lidded jar and shake vigorously.
Continuing whisking while pouring over tomato mixture. Carefully toss to coat all pieces. If the salad needs more dressing, make another 1/2 to whole batch.
Top individual portions of the salad with the croutons.