Boil jumbo shells according to package. Drain and set aside covering with a wet paper towel to keep from drying.
Brown ground meat in a skillet together over medium heat with diced onion. Cook until no pink meat remains. Drain any excess fat.
Thaw spinach in a colander under warm water. Press to remove excess water.
In a large bowl, mix together parmesan cheese, ricotta cheese, spinach, meat, onions and spices including salt and pepper.
Take meat and cheese mixture and gently stuff into shells. Line a large baking pan or two smaller baking pans (freeze one!) with shells.
Cover shells with tomato sauce. Top with slices of fresh mozzarella. Bake at 375˚ for about 20-25 minutes or until cheese is melted and sauce it bubbling in the center. Garnish with fresh parsley before serving.