Place each chicken breast half between 2 sheets of heavy-duty plastic wrap; pound to 1/2-inch thickness using a meat mallet or small heavy skillet. Sprinkle chicken with 1/4 teaspoon salt and 1/4 teaspoon pepper. Combine cheese and flour in a shallow dish. Dredge 1 side of each chicken breast half in cheese mixture.
Heat 1 teaspoon oil in a large nonstick skillet over medium-high heat. Add 2 chicken breast halves, cheese side down; cook 4 minutes on each side or until done. Repeat procedure with remaining 1 teaspoon oil and chicken breast halves. Remove from pan; keep warm.
Coat pan with cooking spray. Add onion; sauté 2 minutes. Stir in broth and vinegar; cook 1 minute or until liquid almost evaporates. Add tomatoes, remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, and oregano; cook 2 minutes.
Wine note: These chicken breasts have a piquant Italian flavor. I love to serve them with an Italian red made from the sangiovese grape. Try the incredible Marchesi di Frescobaldi "Campo ai Sassi" Rosso di Montalcino 2004 (Montalcino, Tuscany, Italy), $20. -Karen MacNeil