Preheat the oven to 325 degrees F. Put the quinoa, chopped onion, and 2 cups of water in a pan with a lid. Bring to a boil, then reduce heat to low and simmer until the quinoa is done, about 15 minutes.
While the quinoa is cooking, place the broccoli in a pan with about an inch of water. Put the lid on the pan and steam over medium heat until the florets are tender, but still bright green.
During this time you can also prepare the breadcrumbs. Heat the vegan buttery spread and the olive oil in a frying pan over medium heat. Add the gluten free bread crumbs and garlic salt to taste.
Cook the breadcrumbs until they turn golden brown, stirring often. Don't walk away, they will burn quickly if you do! Once they are golden brown, remove from the heat and set aside.
When the quinoa is done, place it in a casserole dish. Drain the broccoli and add it to the casserole dish.
In a separate pan, (you can just rinse the broccoli pan and re-use it), melt the 3 tablespoons of vegan buttery spread over medium heat Add the gluten free flour and stir to combine. Slowly add the dairy free milk, stirring constantly. The sauce should start to thicken. Add the Daiya cheese and the salt and pepper. Stir. The sauce should be thick and creamy, like what you would put on macaroni and cheese. If it gets too thick, just add a bit more dairy free milk.
Pour the sauce over the quinoa and broccoli. Stir. Sprinkle the breadcrumb mixture on top.
Place in the casserole in the preheated oven, uncovered, for about 15 minutes, just to heat everything through and let the flavors combine.
Serve immediately.