Serve these savory, filled chicken breasts over steamed greens like escarole or Swiss chard.
Place each piece of chicken between two 12-inch squares of plastic wrap. Using a meat pounder, pound to a 1/4-inch thickness.
Spread 1/4 cup onion jam over each breast, and fold breast in half. Season both sides with salt and pepper.
Coat a saute pan with cooking spray, and set over medium-high heat. Place chicken in pan; cook until golden on bottom, about 2 minutes. Turn, and cook until the other side is golden, about 3 minutes.
Add wine, and cook 1 minute. Add stock; reduce heat to medium. Cover; cook until chicken has cooked through, 5 to 6 minutes. Transfer the chicken to a plate.
Add balsamic vinegar to pan; turn heat to high. Reduce liquid to 1/2 cup, 7 to 10 minutes. Drizzle sauce over chicken, and serve.