Wrap 3-4 Gold beetsin foil and roast at 425 until tender, about an hour. Peel and cut into thin slices.While the beets are cooking, simmer 1 1/4 C. cider vinegar, 6 T. water, 1 T. mustard seed, 1 t. cumin seed, and 1 t.whole allspice berries with 1 t. sugar for 15 minutes. Add 2 small red onions, cut into 1/2″ thick wedges and cook for 2 minutes. Use sieve to drain the onions and spices (reserving the liquid), then discard the spices.
Cut thick slices of 2-3 tomatoes and sprinkle with salt and olive oil. Toss with the beets and onions plus pickling liquid to taste.