Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper for easy cleanup.
Toss the cubed sweet potatoes with 1 tablespoon olive oil, cumin, paprika, garlic powder, chili powder (if using), and a pinch of salt and pepper. Spread them in a single layer on the baking sheet.
Roast for about 15-20 minutes, then give them a flip. They should be just tender and slightly caramelized around the edges.
While potatoes roast, pat the salmon dry and season with a little salt, pepper, and a light drizzle of olive oil. Place on another baking sheet or a sheet lined with foil.
Bake the salmon in the oven for 10-12 minutes, depending on thickness. It should be flaky and opaque in the center.
In a small bowl, whisk together lime juice, honey, yogurt or sour cream, and chopped cilantro to make a bright, creamy dressing. Season with a pinch of salt.
Warm the black beans and corn in a small pot or in the microwave until heated through.
Assemble: divide roasted sweet potatoes, salmon, black beans, corn, and avocado slices into four bowls. Top with tomatoes and red onion if using.
Drizzle with the lime-yogurt dressing and finish with extra cilantro or fresh lime wedges on the side.
Serve immediately. If you like a little extra zing, a few drops of hot sauce can be stirred into the dressing.