Combine the onion, bell pepper, cumin, garlic powder, chili powder, beans, tomato sauce, fire-roasted tomatoes, water, salt (taste the mixture prior to adding the quinoa, adding salt to taste), and quinoa to a 6-quart slow cooker, stirring to combine. Cover and cook on high for 3 hours or on low for 6 hours, or until the quinoa is cooked through.