Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Pat the chicken breast dry with a paper towel and cut it into 1-inch bite-sized pieces.
Mince the garlic cloves finely.
In a large mixing bowl, combine the chicken pieces, broccoli florets, olive oil, minced garlic, sea salt, black pepper, and dried oregano.
Toss everything thoroughly until the chicken and broccoli are evenly coated in the oil and seasonings.
Spread the mixture in a single layer on the prepared baking sheet, ensuring there is space between pieces so the broccoli roasts rather than steams.
Roast in the center of the oven for 18 to 22 minutes, tossing halfway through, until the chicken is cooked through and the broccoli edges are golden and crispy.
Remove from the oven and immediately squeeze the juice of half a lemon over the hot tray before serving.