Into a large pot, add olive oil and onion. Saute until translucent and then add in pureed tomatoes. Season with salt, pepper and basil. Bring it up to a boil and then lower to a simmer. Cook for 1 1/2 hours, stirring occasionally.
Eggplant
Slice your eggplant into rounds that are about 3/4 in thick. Spray with Avocado oil and season with salt and pepper. Grill them on both sides until tender.
Place the grilled eggplant on a plate and cover with aluminum foil. It will release some of it water and then you can pat them dry with a paper towel.
Assembly
Preheat the oven to 400℉.
Into a baking dish, add sauce to coat the bottom. Add a slice of eggplant, some sauce and mozzarella, another slice of eggplant, sauce and mozzarella, and a final slice of eggplant. Top with more sauce and continue until you have used up all the eggplant. Top with more shredded mozzarella and bake for 10-15 mins until the cheese has melted and the sauce is slightly bubbling.