Those tacos look amazing, and what a great use for leftovers! I would love to make brisket for RS, or even chicken, but with a vigilant vegetarian in the family, everything goes more smoothly when meat and fish aren't around. So here's my leftover hack: make extra matzah balls and then use them as dumplings in mushroom stew or tossed with some other roasted veggies that are lightly spiced and sauced. They would also make excellent 'chicken n' dumplings,' I assume, though I've never made it.