Thinly slice onion and mince garlic.
Heat olive oil in pot over medium-high heat.
Add onions and cook until translucent, about 5-10 minutes.
Turn heat down to low and add minced garlic. Cook for 1-2 minutes until fragrant.
Add all 4 cans of tomatoes and sauce.
Rinse cans with a small amount of water each and add to pot (to get all of the tomatoes/sauce out of cans). Add roughly 2 cups of water total.
Add basil, oregano, garlic powder, salt, pepper, and parmesan cheese. Stir well.
Add more water if you want to make the sauce thinner.
Bring to boil, then reduce to low. Cook for 1 hour, stirring every 5-10 minutes to make sure it doesn't stick.