To make the vinaigrette, combine the vinegars, shallots, garlic, salt, and pepper in a medium bowl and whisk to combine. Slowly add the olive oil in a steady stream, whisking to combine. Set aside to allow flavors to come together while you prepare the remaining ingredients. Add chopped herbs, if using, and whisk to combine.
On a large platter, arrange the tomato and mozzarella slices in overlapping fashion and scatter the sliced onions over the top. Drizzle the vinaigrette over all and serve immediately, garnished with the pine nuts and edible flowers, if desired.
Note: You may substitute other herbs to your liking just make sure to use "soft" herbs, such as chervil, basil, chives, tarragon, mint, parsley, cilantro, etc.