1. Sort beans for debris, then rinse. Bring beans and 1 quart water to a boil over high heat in a 5- to 6-quart pan. Cover, boil for 2 minutes, and remove from heat. Beans are ready to cook after soaking for 2 hours, but are more digestible after 4 hours. To use, drain and rinse.
2. In a 4- to 5-quart pan over high heat, bring 2 cups water, 1 cup chopped onion, cilantro, chili, garlic, 1/2 teaspoon cumin, and oregano to a boil. Reduce heat and simmer, covered, for 10 minutes. Whirl in a blender until smooth.
3. In pan combine onion mixture, broth, and soaked beans. Bring to a boil over high heat, then reduce heat and simmer, covered, for 45 minutes.
4. Meanwhile, in a 3- to 4-quart pan over medium heat, frequently stir bacon and 1 1/2 cups onion until onion is deep golden, about 20 minutes. Stir in wine and set aside.
5. On a rack in a 12- by 15-inch broiler pan, broil tomatoes 2 inches from heat, turning until blackened all over, about 15 minutes. Coarsely chop; set aside.
6. Add bacon mixture, tomatoes, minced marjoram, and vinegar to beans. Simmer, uncovered, stirring often, until beans are tender to bite and enough liquid evaporates to make a thick stew, 30 to 40 minutes. Add salt and pepper to taste.
7. While beans simmer, sprinkle lamb all over with salt, pepper, and remaining cumin. Broil 2 inches below heat, turning once, until done to your liking, about 8 minutes for medium-rare.
8. Spoon bean mixture into 4 wide soup bowls. Top each with a lamb chop, and garnish with marjoram sprigs.