In a sauce pan, combine vegan butter (or oil) and chopped yellow onion until thoroughly heated and onions are translucent. Add gluten-free flour on low heat, stirring for 3 minutes until fully combined.
Add Oatmilk and bring to a simmer.
Stir in dairy-free cheese until fully melted. Then add garlic powder sea salt.
Mix cheese sauce into your favorite pasta (about a pound), and pour into pie crust. Serve immediately.