Line a skillet with a thin layer of water (or vegetable broth). Sauté onion over high heat until translucent—about two to three minutes. Add chili powder and cumin, and stir to combine. Then add beans, vegetable broth (or water), and salsa. Bring to a boil, then reduce to low and simmer for ten minutes. Remove from heat and stir in lime juice. Transfer half of the mixture to a blender and puree until mostly smooth. Mix puree back in with soup. Garnish with cilantro, green onions and crumbled corn chips, if desired. You can also drizzle with hot sauce or add cayenne pepper to taste.