Heat the olive oil in your large skillet or pot over medium-high heat. Once hot, add the diced onion and red bell pepper. Cook, stirring occasionally, until the vegetables are softened and develop a slight golden-brown color, about 5 minutes.
Stir in the minced garlic and cook for another 30 seconds or until fragrant, being careful not to burn it.
Add the rinsed quinoa to the skillet along with ground cumin, cayenne pepper, salt, and black pepper. Stir well to coat the quinoa and spices evenly with the oil and vegetables.
Pour in the vegetable broth and give everything a good stir. Increase heat slightly and bring the mixture to a gentle boil.
Once boiling, reduce the heat to low and cover the pot with the lid. Let it simmer for about 20 minutes, or until the quinoa absorbs the liquid and is tender.
Remove the lid and fold in the frozen corn, black beans, and chopped cilantro. Continue cooking on low heat for another 5 minutes, stirring occasionally, until the beans and corn are heated through.
Taste and adjust seasoning with additional salt, pepper, or cayenne pepper as desired.
Serve warm, garnished with extra cilantro and your choice of toppings such as sour cream, shredded cheese, avocado slices, hot sauce, or a squeeze of fresh lime juice. This dish is also delicious wrapped in a tortilla as a burrito.