1. Position oven rack in top position; preheat broiler.
2. Combine flour, salt and pepper in a shallow dish. Place chicken between 2 large pieces of plastic wrap. Pound with the smooth side of a meat mallet or a heavy saucepan until the chicken is an even 1/4-inch thickness. Dip the chicken in the flour mixture and turn to coat.
3. Heat 2 teaspoons oil in a large nonstick skillet over medium-high heat. Add spinach and cook, stirring often, until wilted, 2 to 3 minutes. Transfer to a small bowl.
4. Add 1 teaspoon oil to the pan. Add half the chicken and cook until golden, 1 to 2 minutes per side. Transfer to a large baking sheet. Repeat with the remaining 1 teaspoon oil and chicken; transfer to the baking sheet.
5. Top each piece of chicken with the wilted spinach, marinara sauce and Parmesan. Sprinkle with mozzarella. Broil until the cheese is melted and the chicken is cooked through, about 3 minutes. Serve on rolls.

Yield: 4 servings