Preheat your oven to 425°F (220°C).
Toss the diced sweet potatoes with olive oil, chili powder, cumin, salt, and pepper in a large bowl.
Spread the sweet potatoes out in a single layer on a baking sheet and roast for 25-30 minutes, or until tender and slightly caramelized, stirring halfway through.
While the sweet potatoes are roasting, cook the quinoa by combining the rinsed quinoa and vegetable broth (or water) in a medium saucepan.
Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes or until the liquid is absorbed.
Remove from heat and let it sit covered for 5 minutes, then fluff with a fork.
In a large bowl, combine the cooked quinoa, black beans, roasted sweet potatoes, red bell pepper, red onion, and cilantro.
Drizzle with lime juice and toss gently to combine. Season with additional salt and pepper to taste.
Serve immediately or chill in the refrigerator for 30 minutes to allow the flavors to meld.
Top with diced avocado just before serving.