Preheat the oven to 400°F. Rinse the chicken, pat dry with paper towels, and cut in in half to ensure even cooking. Salt and pepper each piece. Tenderize if desired.
Heat ¼ cup olive oil in a large skillet over medium high heat. Add the diced onions and shallots when oil is hot—sauté for 4-5 minutes or until ingredients are golden. Add the wine, lemon, rosemary, and grapes and cook for another 4-5 minutes on medium heat. Remove the skillet form heat and set aside.
In a separate, large skillet, add a remaining olive oil on high heat and sear the chicken breast on each side for 2 minutes, drizzle a splash of balsamic vinegar over each side as you flip. Sear until chicken lightly caramelized—it does not have to be fully cooked. Keep juices and add to roasting pan for moisture and flavor.
Place ½ of the onion and grape mixture on the bottom of a roasting pan, then place chicken on top with juices from pan. Spread remaining grapes and onions on top. Sprinkle with remaining chopped rosemary, and place the pan in the oven. Roast the chicken for 25-30 minutes.
Remove it from the oven and serve immediately—pair with rice, mashed potatoes, mashed sweet potatoes, polenta, or a light salad!