First, prepare the marinade.
In a small saucepan, combine the low-sodium soy sauce, apple cider vinegar, light brown sugar, ground cumin, ancho chile powder, and ½ cup of water.
Bring the mixture to a boil and let it bubble for 1 minute.
Remove from the heat and stir in the liquid smoke, if using.
Arrange the thinly sliced tempeh in a single layer in a 13x9-inch baking dish (or two, if needed).
Pour the warm marinade evenly over the slices.
Let it cool to room temperature, then cover and refrigerate for at least 2 hours, or preferably overnight for the best flavor.
When you're ready to bake, preheat your oven to 300°F / 150°C.
Line two large baking sheets with parchment paper.
Carefully transfer the marinated tempeh slices to the prepared baking sheets, arranging them in a single layer.
Discard any leftover marinade.
Brush the tops of the tempeh slices with canola oil and sprinkle with smoked paprika, if using.
Bake for 10 to 15 minutes, until the edges start to brown.
Remove from the oven, carefully flip each slice, and brush the other side with a little more oil. Return to the oven and bake for another 5 to 7 minutes, or until the tempeh bacon is crisp and a deep, dark brown.
Keep a close eye on it during the last few minutes to prevent burning.
Don't rush the marinade!
Letting the tempeh soak overnight allows it to absorb all the smoky, savory flavors for a much more delicious result.