Heat oven to 350°F. In medium bowl, combine chopped spinach, 2 tablespoons seasoned bread crumbs, and 2 tablespoons grated Parmesan cheese. Spread mixture evenly among the flounder pieces and roll fillets up. Place fish rolls, seam side down, in a baking dish. Sprinkle diced tomatoes around fish on bottom of pan. Season with salt and pepper.
Bake about 10 minutes, or until fish is almost cooked through. Change oven to broiler setting. Sprinkle flounder with remaining 1 tablespoon seasoned bread crumbs mixed with 1 tablespoon Parmesan cheese, and broil 1 to 2 minutes, or until golden-brown.