Heat oil in 10-inch skillet over medium heat and cook onion, stirring occasionally, until golden, about 7 minutes. Add tomatoes, epazote sprigs, chopped serrano, chorizo and 1 tablespoon Knorr® Chicken flavor Bouillon and cook, stirring occasionally, 2 minutes. Stir in bacon and cook 1 minute; set aside.
Bring beans and water to a slow boil in 6-quart saucepot over medium heat. Stir in reserved vegetable mixture. Cook, stirring occasionally, until heated through, about 10 minutes.
Garnish, if desired, with cilantro and/or panela cheese.