Rinse the quinoa in a strainer. Sometimes it can have a bitter taste on the outside so rinsing gets rid of this.
Heat the oil in a saucepan over medium heat. Stir in the onion and garlic, and cook for a couple of minutes or until onion is soft.
Add the quinoa and vegetable broth to the pan. Add the cumin, cayenne pepper, salt, and pepper. Bring mixture to a boil and then cover, reduce heat, and simmer for 20 minutes.
Stir in lime juice and frozen corn into the pan and simmer for 5 minutes or until corn is heated through.
Finally, mix in the black beans and cilantro. Garnish with chopped avocado if desired.