Rinse the quinoa and cook it in a saucepan with 2 cups of water until tender, about 15 minutes. Fluff with a fork and set aside.
Press the tofu between paper towels or a clean kitchen towel to remove excess moisture, then cut it into 1-inch cubes. Place the tofu and all the chopped vegetables on a large baking sheet. Drizzle with olive oil, sprinkle with salt and pepper, and toss to coat evenly.
Roast at 425°F for 25 minutes, flipping the tofu and vegetables halfway through so they brown on both sides.
While the sheet pan cooks, whisk together the tahini, lemon juice, minced garlic, water, and maple syrup in a small bowl until smooth. Add an extra splash of water if the dressing feels too thick.
Divide the cooked quinoa and fresh spinach among four bowls. Top each with roasted tofu and vegetables, then add avocado slices. Drizzle with tahini dressing and finish with sesame seeds.