Preheat the oven to 425°F (220°C).
In a small bowl, mix brown sugar, paprika, garlic powder, onion powder, smoked paprika, salt, and black pepper to form the BBQ rub.
Pat the chicken thighs dry. Rub them all over with the 1 tablespoon of olive oil, then coat generously with the BBQ rub. Let them rest while the oven heats.
Peel and dice the sweet potatoes into roughly 1/2-inch cubes. Halve and slice the red onion, and chop the red bell pepper into bite-sized pieces.
Toss the sweet potato cubes with a pinch of salt and the 1 tablespoon of olive oil. Arrange them on a parchment-lined baking sheet in a single layer.
Roast the potatoes for about 15 minutes. They should start to soften and brown at the edges.
Meanwhile, heat a heavy skillet over medium-high heat. Add the seasoned chicken thighs skin-side down and cook for 4–5 minutes until the skin is crispy and deeply browned. Flip and cook 2–3 minutes more. The goal is partial searing, not fully cooked through.
Remove the skillet from heat. Transfer the chicken to a plate and set aside. In the same sheet pan with the potatoes, nestle the par-cooked chicken thighs among the pieces, skin side up.
Roast everything together for another 18–22 minutes, until the chicken reaches an internal temperature of 165°F (74°C) and the potatoes are tender.
While the chicken and potatoes finish, heat a second small skillet over medium heat. Add the diced red onion and bell pepper, sautéing for 5–7 minutes until soft and caramelized. If you like, a splash of water or broth can help them soften.
When the hash is ready, taste and adjust seasoning with a pinch more salt or a light squeeze of lime juice if you have it on hand.
Serve the BBQ Rubbed Chicken Thighs atop or beside the sweet potato hash. Optional: finish with chopped fresh herbs like cilantro or parsley for a fresh contrast.