Bring a large pot of salted water to a boil. Add the pasta and cook according to package instructions until al dente.

Reserve 1 cup of pasta water, then drain the pasta in a colander.

In a skillet, heat olive oil over medium heat. Add sliced onions and sauté until they are caramelized, about 10-15 minutes.

Add minced garlic, salt, black pepper, and oregano. Cook for an additional 2-3 minutes until fragrant.

Add the cooked pasta to the skillet with the onion sauce. Toss to combine, adding reserved pasta water as needed to create a sauce.

Serve hot, garnished with grated Parmesan cheese and chopped parsley.