Preheat your oven to 425°F (220°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Wash the potato and dice into small 1/2-inch cubes, then dice the chicken breast into 1-inch bite-sized pieces.
In a large mixing bowl, toss the potato cubes with half of the olive oil, sea salt, black pepper, and garlic powder.
Spread the potatoes in a single layer on the prepared baking sheet and roast for 15 minutes to give them a head start on crisping.
While the potatoes roast, use the same mixing bowl to toss the chicken, diced bell peppers, and red onion with the remaining olive oil and smoked paprika.
Remove the baking sheet from the oven, add the chicken and vegetable mixture, and toss everything together before spreading it back out into a single layer.
Return the pan to the oven and roast for another 15-20 minutes, or until the chicken is cooked through and the potatoes are golden-brown.
Remove from the oven and immediately sprinkle with fresh chopped parsley and a drizzle of lemon juice before serving warm.