Combine soy sauce (or liquid aminos), apple cider vinegar, brown sugar, cumin, smoked paprika, and water in a small saucepan.
Bring to the boil and allow to boil for 1-2 minutes, and then turn off the heat. Add the liquid smoke if you are using.
Arrange the tempeh slices in a single layer in a casserole dish. Pour the marinade over the top, and give the dish a shake to ensure it is evenly distributed.
Cover, and allow to marinate for at least one hour, but up to overnight.
Preheat your oven to 150°C / 300°F. Line a baking sheet with parchment paper and brush the parchment with a bit of olive oil.
Drain the tempeh slices and arrange on the baking sheet. Brush the tops with olive oil.
Place into the pre-heated oven and bake for 15 minutes, or until the tempeh is beginning to brown. Flip the slices and bake for 5-10 minutes more, until crisp.
Remove from the oven and let cool slightly before using.