Cook spaghetti according to package instructions, drain and set aside.
In a large pot heat the olive oil over low heat. Saute the onions and garlic for 5 minutes until the veggies begin to soften. Add the mushrooms and saute for an additional 5 minutes.
Add the butter and flour to make a roux and stir into the vegetables to thicken. Add the almond milk and Greek yogurt and stir to combine. Sauce should be thick and creamy. Add salt and pepper to taste.
Toss the spaghetti, parsley, and 3/4 cup of the breadcrumbs into the sauce, and stir well to combine. Top with the remaining breadcrumbs and serve!