Roast the Sweet Potatoes: Preheat your oven to 200°C (400°F). Line a large baking sheet with parchment paper. Toss the cubed sweet potatoes with olive oil, paprika, garlic powder, salt, and pepper. Spread in a single layer and roast for 25 to 30 minutes, flipping halfway, until tender and caramelized.
Prep the Grains and Veggies: While the potatoes roast, ensure your quinoa is cooked and fluffy. Chop the tomatoes, cucumber, onion, and avocado. Rinse and drain the black beans.
Make the Tahini Dressing: In a small bowl, whisk together the tahini, lemon juice, olive oil, and minced garlic. The mixture will thicken at first. Whisk in warm water, one tablespoon at a time, until it reaches a smooth, pourable consistency.
Assemble: Divide the cooked quinoa into 4 deep bowls. Arrange the roasted sweet potatoes, black beans, cucumber, tomatoes, and avocado slices in separate piles over the quinoa.
Serve: Drizzle the lemon-tahini dressing generously over the bowls. Garnish with sesame seeds or fresh parsley if desired. Enjoy warm or at room temperature.