Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Dice the sweet potato into 1/2-inch cubes and slice the carrots into thin rounds to ensure they cook evenly.
Mince the garlic cloves and finely chop the fresh rosemary leaves.
In a large mixing bowl, combine the chicken breast, sweet potatoes, and carrots.
Drizzle with olive oil and add the minced garlic, chopped rosemary, sea salt, and black pepper, tossing thoroughly to coat every piece.
Spread the chicken and vegetables in a single layer on the prepared baking sheet, ensuring they are not crowded so they roast rather than steam.
Roast for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are fork-tender and slightly caramelized.
Squeeze the juice of the half lemon over the entire pan immediately after removing it from the oven to brighten the flavors before serving.