Preheat your oven to 400°F (200°C) and line a large rimmed sheet pan with parchment paper for easy cleanup.
Slice the chicken breast into 1-inch bite-sized pieces and cube the sweet potato into small 1/2-inch cubes to ensure even cooking.
Prepare the vegetables by chopping the broccoli into bite-sized florets, slicing the red bell pepper into thin strips, and cutting the red onion into small wedges.
Arrange the chicken, sweet potato, broccoli, bell pepper, and onion in a single layer on the prepared sheet pan.
Drizzle the extra virgin olive oil over the ingredients and sprinkle evenly with dried oregano, garlic powder, sea salt, and black pepper.
Use your hands or tongs to toss everything thoroughly until the chicken and vegetables are well-coated in the oil and spices, then spread them back into a single layer.
Roast in the center of the oven for 20 to 25 minutes, or until the chicken is cooked through and the sweet potatoes are fork-tender.
Remove from the oven and immediately squeeze the fresh lemon juice over the hot pan to brighten the flavors before serving or packing into containers.