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.

Lightly toast the bread slices (optional, but recommended).

Mash ½ of an avocado on one slice of bread, and if using, spread the other slice with mayonnaise (vegan or regular).

Layer the tempeh bacon slices, lettuce, and tomato slices over the avocado. Top with the other slice of bread.

Serve immediately.