Preheat your oven to 400°F (200°C) and prepare a lightly oiled rimmed baking sheet.

Combine chicken thighs, diced potatoes, and sliced red onion in a large mixing bowl. Add garlic powder, cayenne pepper, salt, and pepper; mix well.

Spread the mixture in a single layer on the baking sheet. Drizzle with olive oil.

Roast in the oven for 25-30 minutes, until chicken reaches 165°F and potatoes are golden brown. Broil for 2-3 minutes for extra crispiness.

Let the dish rest covered with aluminum foil for 5-10 minutes before serving. Garnish with chopped scallions and lemon juice.