Pre-heat oven to 375 degrees. Spray a 8x11 baking dish with natural cooking spray and set aside.
In a large bowl combine quinoa, black beans, corn, olives, tomatoes and spinach.
Spread ¼ cup enchilada sauce on the bottom of the baking dish and layer with half of the corn tortillas. Scoop half of the quinoa mixture onto the corn tortillas. Repeat once ending with quinoa mixture on top.
Pour rest of enchilada sauce on casserole, cover and bake for 30-35 minutes or until enchilada sauce is bubbly.
Let cool and top with cilantro, salsa and avocado as desired.