Heat oil in a sauté pan that has a lid. Add garlic, chili powder, and cumin and cook, stirring, until fragrant, about 30 seconds. Add the tomato paste and cook for another minute, stirring. Add the rinsed quinoa and water, stir, and bring to a boil. Lower heat to maintain a gentle simmer, cover, and cook until liquid is absorbed, 15–20 minutes. Add the beans for the last 5 minutes of cooking.
Dress salad greens and arrange in bowls with tomato slices, avocado, radish, etc. Add a scoop of quinoa & bean and garnish with optional cheese and/or chips or crispy tortilla strips (see headnotes).