Preheat the oven to 400°F (200°C) and lightly spray a 9 x 12 baking dish with cooking spray or oil.
Cook the quinoa: combine 1 1/4 cups quinoa with 1 3/4 cups broth in a medium saucepan and cook according to package instructions until tender; fluff with a fork and set aside.
Make the enchilada sauce: heat 1/2 teaspoon olive oil in a small saucepan over medium-low heat and sauté the crushed garlic 1–2 minutes until golden.
Add the 18-oz tomato sauce, 1/4 teaspoon kosher salt, 1 1/2 teaspoons cumin, 1/4 cup broth, and 1 tablespoon chipotle in adobo to the garlic; stir and add 1–2 tablespoons water if too thick.
Bring the sauce to a boil, then reduce heat and simmer 3–4 minutes to combine flavors; taste and adjust salt or chipotle for spice level.
In a large bowl, combine the cooked quinoa, diced green chiles, drained black beans, corn, 1/4 cup chopped cilantro, and 1/2 cup of the shredded cheese; mix well.
Spread the quinoa mixture evenly into the prepared baking dish, pour the enchilada sauce over the top, and sprinkle with the remaining 1 cup cheese.
Cover the dish with foil and bake at 400°F for 20–25 minutes, until heated through and the cheese is melted.
Remove foil, top with diced avocado, chopped scallions, and the remaining 2 tablespoons cilantro, then cut into 6 pieces and serve immediately.