Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Peel and dice the sweet potato into 1-inch cubes, chop the broccoli into florets, and slice the red bell pepper into thick strips.
Mince the garlic cloves and place them in a small bowl with the olive oil, dried oregano, dried thyme, sea salt, and black pepper, whisking to combine.
Place the chicken breast on one side of the sheet pan and spread the sweet potatoes, broccoli, and bell peppers across the remaining space.
Drizzle the garlic-herb oil mixture over the chicken and the vegetables, using your hands or a brush to ensure everything is evenly coated.
Roast in the oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the sweet potatoes are tender and lightly caramelized.
Remove from the oven and squeeze the fresh lemon juice over the chicken and vegetables before serving.