Heat oil in a large saucepan over medium heat. Add onion and garlic; cook and stir until lightly browned, about 10 minutes. Mix quinoa into onion mixture and cover with vegetable broth; season with cumin, cayenne pepper, salt, and pepper. Bring to a boil; cover, reduce heat, and simmer until quinoa is tender and broth is absorbed, about 20 minutes. Stir in frozen corn and continue to simmer until heated through, about 5 minutes. Mix in black beans and cilantro. Serve with sliced avocado and sprouts and tortillas if desired. * Can use 1/2 cup dry black beans soaked and cooked in 2 cups water for 30 minutes, or in instant pot for 20 minutes.