Preheat oven to 350°.
Place each chicken breast half between 2 sheets of heavy-duty plastic wrap; pound to 1/2-inch thickness using a meat mallet or rolling pin. Sprinkle chicken with salt and pepper.
Place flour in a shallow bowl. Combine mustard and egg in a shallow dish. Combine breadcrumbs, cheese, parsley, chives, and garlic in a shallow dish. Dredge 1 chicken breast half in flour, turning to coat; shake off excess flour. Dip in egg mixture; dredge in breadcrumb mixture. Repeat procedure with remaining chicken, flour, egg mixture, and breadcrumb mixture.
Heat oil in a large ovenproof nonstick skillet over medium-high heat. Add chicken; sauté 2 1/2 minutes or until browned. Remove from heat. Turn chicken over; place pan in oven. Bake at 350° for 10 minutes or until chicken is done. Serve with lemon wedges, if desired.