In an 8x8 baking dish, combine the tamari, rice vinegar, maple syrup, garlic powder, and sriracha.
Add the tempeh and turn to coat completely. Let marinate for 15-30 minutes. While the tempeh is marinating, prepare your other ingredients and the dressing if necessary.
Heat the coconut oil in a large skillet over medium heat. Add the marinated tempeh in a single layer, reserving the extra marinade. Cook for 7-8 minutes, turning once, until golden brown.
Once the tempeh is a deep golden brown, pour in the reserved marinade and stir gently until it has cooked off and thickened around the tempeh.
To assemble the sandwiches, cut the ciabatta rolls in half and spread both sides with some of the tahini ginger dressing. On the bottom slice, layer carrot, spinach, tomato, and avocado before adding about half the tempeh.