Preheat the oven to 425 degrees. Line a baking sheet with parchment paper.
Lay out the Brussels sprouts, sweet potato noodles, and string beans. Drizzle everything with olive oil and season with salt and pepper. On the Brussels sprouts, also season with garlic powder and lightly drizzle balsamic vinegar. On the sweet potato noodles, season lightly with paprika. Toss the Brussels sprouts together to combine with seasonings.
Roast the vegetables for 25 minutes. Check the sweet potato noodles after 10 minutes. If they’re fully cooked, remove and place in a bowl or plate and cover to keep warm. If they’re still crunchy, toss, and continue to cook, checking in 5 minute intervals until they’re done – be careful not to burn.
Assemble the bowls. Divide the veggies into the bowls, along with the quinoa. Top with avocado (if using) and drizzle with tahini.