Core the large tomatoes and stem any cherry or tiny tomatoes. Cut the larger tomatoes into large, evenly sized pieces. To do this easily, first cut the tomatoes crosswise into thick slabs, and then cut the slabs into large dice (3/4 to 1 inch wide). If the tomatoes are very irregularly shaped, just cut them into wedges and then cut the wedges in half. Cut the cherry or tiny tomatoes in half or into quarters. Put all of the tomatoes into a large shallow serving bowl.
Peel the peaches with a paring knife and slice them off the pit into wedges (whatever size you like, depending on the size of your peach). Add the peaches to the bowl. Slice the onion lengthwise as thinly as you can and add it to the bowl, too.
Whisk together the olive oil, 2 Tbs. orange juice, 1 Tbs. balsamic vinegar, 1 tsp. soy sauce, lemon zest, and 1/4 tsp. salt. Pour the dressing over the tomatoes and peaches. Add half of the herbs, season with salt, and toss gently but thoroughly. Taste the juices and add more vinegar, soy sauce, and orange juice if you need to. (You can let the salad sit for a few more minutes and taste and season again if you like.) Before serving, toss again and sprinkle with remaining herbs and the flowers (if using).
If you can, try not to toss the salad until a few minutes before serving—while the flavor improves with sitting, the looks and texture do not. So if you’re putting this out on a buffet, mix it very gently (right in its serving bowl) as close to serving time as possible.