In a large skillet, heat 1 tablespoon oil over medium-high heat. Add half the chicken; cook and stir until browned. Transfer to a 6-qt. slow cooker. Repeat with remaining oil and chicken., Stir broth, vegetables, lemon slices, lemon juice, lemon zest and pepper into slow cooker with chicken. Cook, covered, on low 4-5 hours or until chicken is tender. Stir in rice; heat through.