Place the quinoa and water in a saucepan with salt and bring to a simmer over medium-high heat. Reduce the heat, cover the pot, and simmer for 12 minutes. Remove from the heat, and let stand with the lid on for 10 minutes. Remove the lid and fluff the quinoa with a fork.
Meanwhile, in a large skillet, heat the olive oil over medium heat. Add the scallions and garlic and saute for 3 minutes until the scallions are softened. Stir in the black beans, artichoke hearts, tomatoes with chilies, corn, chili powder, cumin, cayenne, and salt.
Add the quinoa to the skillet and stir until everything is well combined.
Spoon half of the mixture into a 2-quart baking dish and sprinkle over 1 cup of the cheese. Distribute with remaining quinoa mixture over the top, and sprinkle over the other cup of cheese. Bake for 15 to 20 minutes, until hot throughout and the cheese is melted.
While the casserole is baking, put the desired condiments in little bowls. In one bowl, mix together the sour cream and pureed chipotles. In others place the avocado, salsa, scallions, and cilantro. Serve the casserole hot and top as desired.
Notes
This is a perfect dish to make at gatherings as the carnivores can enjoy it as a side, but it's hearty enough to be a vegetarian's main dish.
Try kidney beans or pinto beans instead of the black beans.
Use a shredded Mexican cheese blend instead of the cheddar.