Preheat oven to 400°F. Lightly oil a baking sheet or roasting pan and coat with nonstick spray.
In a large bowl, mix together chicken, potatoes, onion, garlic powder and chili powder and 2 Tbs olive oil. Season with salt and pepper and mix well.
Place chicken, potatoes and red onion in a single layer onto the prepared baking pan.
Roast in the preheated oven until the chicken is completely cooked through, reaching an internal temperature of 165°F, about 25-30 minutes. Then broil for 2-3 minutes to make it crisp.
Remove from oven. Cover with foil and allow to rest for 5-10 minutes while the juices settle before serving.
Serve hot, garnished with chopped scallion and drizzled with lemon juice.
Notes
Optionally: After step 2, you can directly transfer the chicken, potato and spices in a air-tight sealed bag and keep it in the fridge or freezer and pop in the oven when needed.