In a jar combine the lime juice and zest, soy sauce, garlic, cumin, chili flakes and chopped cilantro. Add a tbsp or two of water if it's too thick.
Cut the tofu into 1” cubes and place in a square or rectangular container. Pour over the marinade, seal with a lid, give a few shakes and let marinate for at least 1 hour, or up to overnight, which will give the tofu more time to absorb most of the marinade.
Warm 1 tbsp oil in a large skillet over medium heat and add the pieces of marinated tofu one by one. Brown each side of the tofu for 2 minutes and repeat until all pieces of tofu are cooked.
