Heat oven to 375°F.
Slice red onion (widthwise) into thick rings (about ½ an inch). Arrange on parchment-lined baking tray. Brush with oil and sprinkle with salt and pepper. Turn the onion rings over and repeat on the other side.
Slice the ends off the sweet potatoes and peel them. Slice them widthwise, into ½ inch thick rounds. Arrange them on a parchment-lined baking tray. Brush with oil and season with salt and pepper. Turn the sweet potato slices over and repeat on the other side.
Wash brussels sprouts and pat dry. Trim the ends off the brussels sprouts and slice in half lengthwise (through the stem). Toss in maple syrup, garlic and salt and pepper to taste.
Place the onions, sweet potato and brussels sprouts in the oven for 30 minutes, turning half-way through.
Rinse quinoa in a mesh strainer. Add to a medium-sized pot with 1 cup of water or vegetable broth. Bring to a bowl, reduce heat, cover and simmer gently for 12 to 15 minutes. Turn off burner and let sit for 10 minutes. Fluff with fork.
Place spinach in steamer basket and steam for approximately 5 minutes, until wilted.
Divide cooked quinoa into two bowls. Divide the onions, sweet potato, brussels sprouts and spinach between the bowls. Add 2 tbsp of kimchi or sauerkraut to each bowl (optional). Drizzle the tahini dressing evenly over each bowl and top with sesame seeds and sprouts (optional).