Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Cut the chicken breast into 1-inch bite-sized pieces to ensure they cook quickly and remain juicy.
In a large mixing bowl, combine the chicken pieces, broccoli florets, and corn kernels.
Drizzle the olive oil and lemon juice over the mixture, then sprinkle with oregano, garlic powder, sea salt, and black pepper.
Toss everything thoroughly until the chicken and vegetables are evenly coated in the oil and seasonings.
Spread the mixture in a single layer on the prepared sheet pan, ensuring items aren't overcrowded so they roast rather than steam.
Roast in the oven for 15 to 18 minutes, or until the chicken reaches an internal temperature of 165°F and the broccoli is tender with slightly charred edges.
While the chicken roasts, gently warm your pre-cooked white rice in a small pan or the microwave.
Place the fresh baby spinach in the bottom of a serving bowl and top with the warm rice.
Spoon the roasted chicken, broccoli, and corn over the rice, allowing the residual heat to slightly wilt the spinach before serving.