About 40 minutes before serving: In small bowl, with fork, mix feta cheese, lemon juice, and oregano until smooth. On work surface, with meat mallet or dull edge of French knife, lb. each chicken-breast half to 1/2-inch thickness. With knife or small metal spatula, spread cheese mixture over each breast half to within 1/2 inch of edge. Fold chicken breasts crosswise in half to enclose filling; secure with toothpick. On sheet of waxed paper, mix salt, pepper, and 1 tablespoon flour; use to coat chicken. In 12-inch skillet over medium-high heat, in hot olive or salad oil, cook chicken until golden brown on both sides, turning once. Meanwhile, in cup, mix chicken-flavor instant bouillon, 1 tablespoon flour, and 1 cup water until smooth. To chicken in skillet, add flour mixture, tomato, and spinach; over high heat, heat to boiling. Reduce heat to low; cover and simmer 8 to 10 minutes until chicken is fork-tender and loses its pink color throughout. Remove and discard toothpicks to serve chicken. Makes 6 servings. Each about 275 calories, 11 g fat, 104 mg cholesterol, 745 mg sodium. chick 13