Heat the avocado oil in a large skillet over medium heat. Add the onions and cook until dark in colour, about 15-20 minutes.
Meanwhile, bring a large pot of water to a boil with a scant of salt and cook the spaghetti to your desired firmness (8-10 minutes). Drain and set aside.
Once the onions are caramelized, add the chopped garlic, cook for another few minutes. Add oregano and salt and pepper to taste.
Mix in the whole milk and parmesan cheese. Heat until the cheese has melted. Serve!
Tip: Add a pinch of chili pepper flakes for a little kick!