Bring a large pot of salted water to boil. Cook pasta until al dente, 8-10 minutes. Reserve 2 cups pasta water.
In a large skillet, heat olive oil and vegan butter over medium. Add onions, reduce heat to low, and cook 20-25 minutes until caramelized and jam-like, stirring occasionally. Add sugar, smoked paprika, and garlic powder; stir until incorporated.
Create a chile oil by heating 1 tbsp olive oil in a small saucepan. Add a pinch of chili flakes or cayenne, then remove from heat. Let cool slightly.
In a blender, combine caramelized onions, oat milk, chile oil, dried herbs, salt, and pepper. Blend until smooth and glossy. Deglaze the skillet with 1/4 cup pasta water to loosen browned bits, then stir into sauce.
Return cooked pasta to the skillet. Add 1-2 cups reserved pasta water and sauces, mixing until well-coated. Toss with vegan parmesan and remaining chili oil.
Adjust seasoning and serve immediately.