Heat the olive oil in a large pot over medium heat. Add the onion and cook for 3 minutes until it starts to soften.
Stir in the garlic and red bell pepper. Cook for 2 more minutes until the pepper begins to soften.
Add the chili powder, cumin, cayenne pepper, salt, and black pepper. Stir for 30 seconds to toast the spices.
Pour in the rinsed quinoa, black beans, fire-roasted tomatoes, and vegetable broth. Stir everything together.
Bring the soup to a boil, then reduce the heat to low. Cover and simmer for 20 minutes, stirring once halfway through.
Remove the lid and check that the quinoa is tender. Turn off the heat and let the soup sit for 5 minutes to thicken slightly.
Ladle into bowls and top with fresh cilantro and a squeeze of lime.