Roast the Sweet Potatoes: Preheat oven to 400°F (200°C). Toss diced sweet potatoes with 1½ tablespoons olive oil, smoked paprika, garlic powder, salt, and pepper. Spread in a single layer on a parchment-lined baking sheet. Roast for 22-27 minutes, flipping halfway through, until tender inside with golden, caramelized edges.
Cook the Chicken: Pat chicken cubes completely dry with paper towels. Season with garlic powder, onion powder, thyme, salt, and pepper. Heat 1 tablespoon oil in a large skillet over medium-high heat until shimmering. Add chicken in a single layer and let sit undisturbed for 2-3 minutes to develop a crust. Stir and cook another 4-5 minutes until golden brown and cooked through (165°F internal temperature). Remove from heat.
Prepare the Sauce: In a small bowl, whisk together Greek yogurt, lime juice, sriracha, cumin, smoked paprika, and cayenne pepper until completely smooth. Season with salt to taste. The sauce should be thick but pourable—add a teaspoon of water if needed to thin slightly.
Warm the Grains: If using refrigerated rice or quinoa, warm it gently in the microwave or on the stovetop with a splash of water. Fluff with a fork before using.
Assemble the Bowls: Divide warm grains among four serving bowls. Arrange roasted sweet potatoes, pan-seared chicken, and any additional vegetables in separate sections on top of the grains.
Finish and Serve: Drizzle the tangy yogurt sauce generously over each bowl. Garnish with fresh cilantro, additional lime wedges, and sliced avocado if desired. Serve immediately while still warm.