Start by rinsing the quinoa thoroughly under cold water in a fine mesh strainer to remove any bitterness. After rinsing, drain it well and set it aside. Finely chop the bell pepper, red onion, and mince the garlic. Gather the black beans and diced tomatoes.

In a spacious crockpot, combine the rinsed quinoa, black beans, diced tomatoes (with juices), corn, bell pepper, red onion, and minced garlic. Sprinkle in the ground cumin, chili powder, and smoked paprika. Stir everything together.

Pour in the vegetable broth or water into the crockpot mixture. Stir gently to combine all ingredients and ensure the quinoa is submerged in the liquid.

Add salt and pepper to taste in the crockpot, adjusting according to your flavor preferences. Give everything a final stir to blend in the seasoning well.

Cover the crockpot and set it on low for 4 to 6 hours, or high for 2 to 3 hours. Check the mixture at the end of the cooking time; the quinoa should be fluffy and tender.

Approximately 15 minutes before serving, stir in the shredded cheese of your choice. Allow the cheese to melt into the casserole.

If the casserole appears too dry upon serving, add a splash of vegetable broth or water, mixing gently to distribute the added liquid.

Once cooked and the cheese is melted, fluff the casserole with a fork. Taste and adjust the seasoning as necessary. Serve hot with optional toppings.