Rinse quinoa thoroughly with cold water in a fine-mesh strainer, let drain.
In a medium saucepan over medium heat, bring vegetable stock, quinoa, cumin, cayenne pepper, salt and pepper to a boil. Cover and simmer on low 20 minutes, or until all of the liquid is absorbed. Remove from heat and let stand for 5 minutes. Fluff with a fork. Stir frozen corn into the saucepan, and continue to simmer about 5 minutes until heated through. Mix in the black beans and cilantro.
While the quinoa is simmering, heat the oil in a medium saucepan over medium heat. Stir in the onion and garlic, and saute until lightly browned. Transfer to a large bowl.
Add the quinoa, bell pepper and cherry tomatoes to the onion mixture and toss to combine.