Preheat your oven to 350F. In a small saucepan over high heat, bring the quinoa and water to a boil, then cover and reduce the heat to low for 15 minutes, until the quinoa is tender and the moisture has been absorbed. Fluff with a fork and set aside.
While the quinoa is cooking, saute the chopped onion in a large saute pan (preferably with a lid) in the coconut oil until tender, about 5 minutes. Add in the broccoli florets and a splash of water to prevent sticking, then cover the pan and allow to steam for about 10 minutes, or until the broccoli is fork-tender.
To prepare the "cheese" sauce, combine all of the ingredients in a blender and blend until completely smooth and creamy. Keep in mind that this sauce will be diluted over the entire batch of quinoa and broccoli, so it may be on the salty-side to taste.
If your large saute pan is oven-safe, you can save yourself from cleaning an extra dish by assembling the casserole directly over the sauteed onion and broccoli. Add in the cooked quinoa, then pour over the cheese sauce, and stir to mix well. Adjust any seasonings to taste, then use the back of a large spoon to smooth the top.
Bake at 350F for 30 minutes, or until bubbly hot! Serve immediately, and store any leftovers in the fridge for up to 3 days.