In a small bowl, combine the olive oil, juice of one lemon, minced garlic, chopped rosemary, dried oregano, salt, and pepper to create a marinade.
Place the chicken breasts in a large resealable plastic bag or a shallow dish. Pour the marinade over the chicken, ensuring it's well-coated. Seal and marinate for at least 30 minutes, or up to 2 hours in the refrigerator for more flavor.
On a large sheet pan, spread out the cherry tomatoes, sliced bell pepper, and red onion. Drizzle with olive oil and season with salt and pepper. Toss to coat.
After marinating, remove the chicken from the bag and place it on the sheet pan with the vegetables. Lay lemon slices on top of the chicken for added flavor.
Bake in the preheated oven for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F (75°C) and is golden brown. The vegetables should be tender and slightly caramelized.
Remove the sheet pan from the oven and let the dish rest for 5 minutes. Garnish with additional fresh rosemary sprigs if desired.
Notes
Marinate the chicken for longer for enhanced flavor.