On medium-low, put olive oil in your pan until heated, then add the green pepper and cook for a few minutes until a bit soft. Next, add your onion and zucchini and cook until a bit soft.
Next you will add the minced garlic and sauté until slightly browned. Add in the whole tomatoes and the puree and let them heat up while you break the tomatoes with a wooden spatula. After the sauce has heated up and has started bubbling, add in the tomato sauce and spices and brown sugar.
With the heat still on medium-low, let the sauce heat up to a simmer before turning down to low. Let it simmer on low until the extra liquids have simmered out of the sauce. This could take anywhere from 20-40 minutes.
When the extra liquids have evaporated, your sauce is ready to use!