Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Scrub the sweet potato and cut it into 1-inch cubes, then toss them with half of the olive oil and a pinch of sea salt.
Spread the sweet potato cubes onto the baking sheet and roast for 10 minutes.
While the potatoes roast, mince the garlic and whisk it in a small bowl with the remaining olive oil, thyme, rosemary, salt, and pepper.
Pat the chicken breast completely dry with a paper towel and coat it thoroughly with the garlic-herb oil mixture.
Move the sweet potatoes to one side of the tray and place the chicken breast on the other side.
Roast for 20 to 25 minutes or until the chicken reaches an internal temperature of 165°F and the potatoes are golden.
While the chicken finishes, steam the broccoli florets in a steamer basket for 4 to 5 minutes until tender-crisp.
Remove the chicken from the oven and let it rest for 5 minutes before slicing to ensure the juices redistribute.
Plate the sliced chicken with the roasted sweet potatoes and broccoli, then drizzle the lemon juice over the vegetables for a bright finish.