In another medium sauce pan, warm 2 TBS olive oil
Add the rest of the diced onion, saute until tender and translucent
Add 1 minced garlic clove, saute for 30 seconds
Add the spinach and saute until wilted, remove from heat
In a large bowl, mix together ricotta cheese, 1.5 cups grated mozzarella cheese, and the Parmesan cheese
Add egg and remaining spices - salt, pepper, oregano, Italian seasonings - and mix all together
Add sauteed spinach and onions, and mix together
Now you will assemble the stuffed shells
For the Stuffed Shells:
Preheat oven to 350 degrees
Spray the bottom of a 9x13 ovenproof pan
Stuff one of the jumbo pasta shells with 1 to 1.5 TBS cheese/spinach mixture, lay in pan
Continue to stuff each shell until you either run out of shells or cheese/spinach
Once the pan is full, pour the butternut sauce all over the stuffed jumbo shells
Place in oven and bake for 20 minutes
Remove from oven and sprinkle the remaining mozzarella cheese over it
Return to oven and bake for 5 to 10 more minutes until cheese is completely melted.