1. On a sheet of wax paper, sprinkle the chicken w. vinegar and thyme. In a large non-stick skillet, heat the oil. Cook the chicken until browned and cooked through, 4-5 min. on each side. Transfer to plate.
2. Sprinkle the flour and oregano over the pan juices; cook, stirring constantly, 1 min. Gradually whisk in the milk; cook, whisking constantly, until thick and bubbling, 2-3 min. Stir in veggies and cheese and lemon juice. Reduce the heat and simmer until cheese melts, abt 2 min. Place the rice on a large platter; top with chicken. Spoon the sauce over the chicken.