Preheat your oven to 400°F (200°C).
In a small bowl, mix the lemon juice, olive oil, mixed herbs, salt, and pepper to create the marinade.
Place the chicken breast in a shallow dish and pour half of the marinade over it. Allow it to marinate for at least 15 minutes.
Meanwhile, dice the sweet potato into evenly sized cubes and toss them with a little olive oil, salt, and pepper.
Arrange the broccoli florets on a baking sheet and drizzle with the remaining olive oil, salt, and pepper.
Place the marinated chicken and sweet potato cubes on another baking sheet. Drizzle any leftover marinade over the chicken if available.
Roast the chicken, sweet potato, and broccoli in the oven simultaneously. Roast the broccoli for about 20 minutes until crispy on the edges, and the chicken and sweet potato for about 25 minutes or until the chicken is cooked through and the sweet potatoes are tender.
Serve the roasted chicken alongside the crisply roasted broccoli and sweet potato, garnished with a squeeze of fresh lemon if desired.