Cut pork into slices, 1/4" thick. Place pork in plastic bag. Add dressing, turning to coat. Tie bag securely and marinate at least 15 minutes but no longer than 1 1/2 hour. Remove pork from marinade. Brown pork in oil in nonstitck skillet. Pour off drippings. Add tomatoes and spinach to pan. Cover tightly and cook over Medium-High heat for 2-3 minutes or until spinach is wilted. Pour off liquid. Meanwhile, remove soft center from bread to form boats. Spoon 1 cup of pork mixture into each boat. Sprinkle each with equal amount of cheese.
