Asian Slaw: Combine green cabbage, red cabbage, and carrots and toss in a medium serving bowl. Whisk together rice wine vinegar, sugar, lime juice, ground ginger, and salt and pour over salad mixture. Toss and chill until serving.
Sweet Potato Wedges: Cut each sweet potato into eighths. With a pastry brush, coat each piece lightly with canola oil. Bake in a preheated 425 degree F oven for 20 minutes or until tender. Set aside and keep warm until serving.
Tempeh: Cut each tempeh cake in half and then cut each piece in two lengthwise. You should end up with 4 semi-square pieces. Score each piece on both sides, diagonally, about 1/8-inch deep. Repeat scoring in opposite direction to create a diamond pattern. In a medium saucepan, bring 2 cups water to boil, add tempeh cakes, and steam for 5 minutes. Remove from heat and place tempeh in a flat bowl or square baking pan and pour soy sauce over top, making sure each piece gets coated. Let set for 5 minutes.
Arrange tempeh on lightly oiled baking sheet. With a pastry brush, lightly coat the top of each tempeh cake, top and bottom, with barbecue sauce.
Caramelized Onions: In a medium non-stick skillet, heat canola oil over medium-high heat and add sliced onion. Saute onion until translucent, add the brown sugar, and continue cooking another 1 to 2 minutes. Remove from heat.
Assembly: Place 1 or 2 slices of BBQ tempeh in a whole grain sandwich bun. Top with caramelized onions. Place on a plate with 4 sweet potato wedges and a serving of Asian slaw. Have a small bowl of barbecue sauce on the side.