1. Prepare grill. In medium-size skillet, heat 1 tablespoon oil over medium-high heat. Add onion and red pepper; saute 5 minutes. Add spinach, 1 teaspoon rosemary, 1/2 teaspoon salt and 1/4 teaspoon pepper; cook 3 minutes. Remove from heat; let cool slightly. Stir in cheese.
2. For rub, in small cup, combine 1 tablespoon oil, 2 teaspoons rosemary, 1/2 teaspoon salt, 1/4 teaspoon pepper.
3. In each breast, cut a pocket horizontally through thicker side. Fill each with 3 to 4 tablespoons spinach stuffing. With 2 toothpicks, secure pocket closed. With fingers, spread rub on both sides of each chicken breast.
4. Grill 10 to 12 minutes per side or until instant-read thermometer inserted in chicken registers 170 degrees F. Makes 6 servings.