Preheat your oven to 400°F (200°C) and line a baking tray with parchment paper.
In a small bowl, combine lemon juice, minced garlic, mixed herbs, salt, and pepper.
Place the chicken breast in a bowl and pour half of the lemon herb mixture over it, ensuring it is evenly coated. Let marinate for 15 minutes.
Dice the sweet potato into cubes and cut broccoli into florets. Place them in a separate bowl.
Drizzle olive oil and the remaining lemon herb mixture over the vegetables, tossing to coat evenly.
Arrange the vegetables on the lined baking tray in a single layer.
Nestle the marinated chicken breast among the vegetables.
Roast everything in the preheated oven: Start with the vegetables for 10 minutes, then add the chicken and continue roasting for about 20-25 minutes or until the chicken is fully cooked and the vegetables are tender and crispy.
Remove from oven, let rest for 5 minutes, and serve your delicious, balanced meal.