Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Peel and dice the sweet potato into 1/2-inch cubes, and slice the cremini mushrooms into thick pieces.
Cut the chicken breast into bite-sized chunks and place them on the baking sheet along with the sweet potatoes and mushrooms.
Drizzle the olive oil over the chicken and vegetables, then sprinkle evenly with smoked paprika, garlic powder, sea salt, and black pepper.
Toss everything together with your hands or a spatula until well-coated, then spread into a single, even layer.
Roast in the center of the oven for 20-22 minutes, or until the chicken is cooked through and the sweet potatoes are tender.
Add the chopped kale to the baking sheet during the last 3 minutes of roasting, tossing it slightly to wilt.
Remove from the oven, drizzle with fresh lemon juice for brightness, and serve immediately in a large bowl.