Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Peel and dice the sweet potato into 1/2-inch cubes. Toss them on the baking sheet with half of the olive oil, half of the sea salt, and half of the black pepper.
Roast the sweet potatoes for 10 minutes to give them a head start.
While the potatoes roast, mince the garlic cloves and finely chop the fresh rosemary and thyme.
In a small bowl, whisk together the remaining olive oil, lemon juice, minced garlic, rosemary, and thyme.
Season the chicken breast with the remaining salt and pepper, then coat it thoroughly with the herb and lemon mixture.
Remove the baking sheet from the oven. Move the potatoes to one side and place the chicken breast in the center. Add the broccoli florets to the remaining space, drizzling them with any leftover herb oil.
Return the sheet to the oven and roast for 18-22 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender.
Let the chicken rest for 5 minutes before slicing to ensure it stays juicy, then serve alongside the roasted vegetables.