1. In a large pot cook onion, garlic and tomatoes on medium-high heat for 3 minutes. Stir often.
2. Add beans, potatoes and water. Bring to a boil, then reduce to low-medium heat. Cover and continue to cook slowly for 20 minutes.
3. Add cilantro, cumin and lime. Stir and continue to simmer for 10 minutes.
4. Serve warm; sprinkle cilantro on top.