In an ovenproof baking dish, combine the cherry tomatoes, red onion, half the olive oil and half the Herbes de Provence. Season with salt and pepper, and toss to coat evenly.
Brush the chicken breasts with the remaining olive oil and season with the remaining Herbes de Provence, salt and pepper. Nestle the chicken breasts into the vegetables in the dish.
Place the dish into the hot oven to bake for 15-20 minutes, or until the chicken is cooked through and the tomatoes are beginning to blacken and release their juices.
5. Remove from the oven and serve immediately. Serve with a side salad (optional).