Bring water, quinoa, garlic, and onion powder to a boil in a saucepan. Reduce heat to medium-low, cover, and simmer until quinoa is tender and water has been absorbed, about 15 minutes.
Preheat oven to 350 degrees F (175 degrees C). Prepare a 9x13-inch baking dish with cooking spray.
Whisk milk and eggs together in a large bowl. Stir Cheddar cheese and processed cheese food into quinoa mixture until cheeses begin to melt; season with salt and black pepper. Mix quinoa mixture into milk mixture. Transfer quinoa-milk mixture to the prepared baking dish; top with panko bread crumbs.
Bake in the preheated oven until topping is lightly browned, 30 to 35 minutes.
