In a pan, heat 2 teaspoons of the oil over medium-high heat. Add the tempeh to the pan, and fry for 2 to 3 minutes, or until browned on one side, then flip and brown the other side, 2 to 3 minutes. Re-move the tempeh from the pan, and set aside.

Add the onion to the same pan and saute for 4 to 5 minutes, or until slightly browned and soft. So as to not set yourself on fire, turn off the flame, and add the bourbon to the pan. Now let the bourbon simmer over medium heat for 1 minute, or until reduced by half.

Stir in the brown sugar, and simmer until it dissolves, about

1 minute. Add the vegetable stock, and simmer for 2 to 3 more minutes. Stir in the arrowroot slurry, continuing to simmer for about 1 more minute.

When the sauce begins to thicken, add the tempeh to the pan and coat it with the sauce. Cook for 1 to 2 more minutes, or until the sauce reduces to a glaze. Season with salt and pepper to taste.

Time for assembly. If using the smoked cheddar sauce, spread it on the inside of the buns. Assemble the sandwiches from the bottom up in the following order: 1 bun half, 1 piece of tempeh, a little of the bourbon sauce and onions, a few spinach leaves, 1 tomato slice, a pinch of salt, and the other bun half.