Preheat the oven to 400 degrees F.
To make the quinoa: use your instant pot to speed the process. Rinse the quinoa in a mesh strainer for 1 minute or so to remove the film.
Add quinoa to instant pot and cover with 1 1/2 C. water. Put the lid on the instant pot and close the valve; set the time for 1 minute (high pressure/manual) and after it beeps, allow 10 minutes for the pressure to release before removing the lid.
If you do not have an instant pot, cook the quinoa to the package directions.
Place a layer of parchment paper on a rimmed cookie sheet and spread the broccoli in a single layer. Drizzle with olive oil and sprinkle with salt. Place the rimmed cookie sheet in the oven and roast the broccoli for 10-15 minutes or until soft. Then remove and set aside.
Melt the 1 Tbsp butter in the skillet over medium, and add the breadcrumbs - stir until lightly toasted, 2-3 minutes. Put in a bowl and set to the side for later.
Melt the 2 Tbsp butter in the skillet over medium heat; whisk in the flour until a thick paste forms, and then gradually add the milk and stir frequently until the sauce thickens up nicely - 4-5 minutes.
Stir in the greek yogurt, 1 C. of the cheese, broccoli and quinoa and combine well.
Season the mixture with salt and pepper, then pour into a greased baking dish and sprinkle with the remaining 1/2 C. cheese.
Sprinkle the toasted bread crumbs atop the casserole dish.
Turn the oven down to 350 degrees F, and bake 10-15 minutes or until cheese has melted and bread crumbs on top have browned nicely.