Heat the oven to 425°F with a rack in the middle position. Set a large sheet pan on the counter so it is ready for the vegetables.

Put the sweet potato pieces and red onion wedges on the sheet pan.

Drizzle 2 tablespoons of the olive oil over the vegetables. Sprinkle them with 1 teaspoon of the chili powder, the cumin, 3/4 teaspoon of the salt, and the black pepper.

Toss the vegetables right on the sheet pan until they are evenly coated. Spread them into a single layer so the pieces can brown instead of steam.

Slide the sheet pan into the oven and roast for 15 minutes.

Pull out the sheet pan and stir the vegetables with a spatula. Return the pan to the oven and roast for 10 to 12 minutes more, until the sweet potatoes are tender in the center and browned at the edges.

While the vegetables roast, rinse the quinoa in a fine-mesh sieve under cold water for about 30 seconds. Let the extra water drain away.

Put the rinsed quinoa into a medium saucepan. Add 2 cups of water and 1/4 teaspoon of the salt.

Set the saucepan over medium-high heat and bring the water to a boil.

Cover the saucepan, turn the heat down to low, and cook for 15 minutes. The quinoa is ready when the water is absorbed and the grains look puffed and soft.

Turn off the heat and let the covered saucepan stand for 5 minutes. This short rest helps the quinoa finish steaming without sticking.

Put the drained pinto beans into a small skillet. Add the remaining 1 tablespoon olive oil, the remaining 1/2 teaspoon chili powder, the remaining 1/4 teaspoon salt, and 1/4 cup water.