In a large bowl, whisk together the tahini, rice vinegar, pure maple syrup and soy sauce until well combined. Set aside.
Cut the tempeh into bite size pieces. I prefer to cut it in half lengthwise, and then cut into 1-2 inch squares or rectangles.
Add the tempeh to the marinade bowl and gently stir to make sure all the tempeh pieces are covered in the sauce. Cover and place in the refrigerator for 30 minutes while you prepare the potatoes and brussels sprouts.
Trim and halve the brussels sprouts. Wash, dry and quarter the potatoes.
Preheat the oven to 400 degrees and line a large sheet pan with parchment paper. If your pans are small you may need two.
Add the marinated tempeh to the pan, reserving the sauce for once it's done cooking. Add the brussels sprouts and quartered potatoes as well. Spray the brussels and potatoes very lightly with oil, or omit if you are avoiding oil.
Bake for 15 minutes. Remove, give the potatoes and brussels a shake and flip the tempeh over. Return to the oven and bake for 20 more minutes.
Remove from the oven and check the potatoes. Once the potatoes are cooked through, you are done. If you have large potatoes, they may take a little longer to cook. In that case, simply remove the cooked tempeh and brussels from the oven and allow the potatoes to cook a little longer.
Now brush some of the marinade onto the tempeh, drizzle a little on each serving of potatoes and brussels sprouts, and serve.