1. Preheat the oven to 350°F. Pound the rosemary leaves with a pinch of salt in a pestle and motar of flavor shaker. Mix with the olive oil and half the lemon juice and zest.
2. Lay the chicken on a chopping board. Slice one of the breats horizontally, as if you were going to cut it in half. Cut it 80 % of the way through, then open it up like a book. Flatten it out with the heel of your hand and repeat with the other three.
3. Pour the rosemary marinade over the chicken and put to one side to marinate for a few minutes. Make the dressing by mixing the mustard with the rest of the lemon juice and twice as much olive oil. To roast your tomatoes, place on a tray, season and roast for 20 minutes.
4. Bring a large pan of salted water to the boil and cook beans for 5 minutes. Drain and toss them in the mustard dressing, then add the roasted tomatoes.
5. Preheat a griddle pan or barbeque. Grill the chicken breasts for 2 1/2 minutes on each side. Check they're cooke through and serve with the warm beans and tomatoes.