Preheat oven to 400°F.
Boil pasta shells as per instructions. You want to under-cook slightly since it'll be further baked. Drain and once cool enough, arrange in a large baking dish.
In a large skillet (with tall sides) or pot, heat up oil and add ground meat. Let brown and mix evenly to break it up.
Add chopped onions and garlic.
Add tomatoes, tomato paste, salt, pepper, sugar, herbs. Add a bit of water to get the rest of the tomato out of the can. Let simmer for 15 min. Taste and adjust seasoning accordingly.
Mix all the ingredients together for the ricotta cheese mixture.
Use a spoon to stuff the shells with the cheese mixture. Arrange neatly.
Pour meat sauce on top of the shells.
Layer the mozzarella on top.
Bake in oven for about 30 min. Optionally, you can turn the broiler on at the end for around 5 min til the cheese gets crispy and bubbly.
Enjoy!