Sprinkle roast with 1 teaspoon salt and 1 teaspoon pepper.
Brown roast on all sides in hot oil in a Dutch oven over medium-high heat. Add 12 cups water, and bring to a boil; cover, reduce heat to low, and simmer 2 hours.
Remove roast from broth, reserving broth; cool 15 minutes. Shred roast, and return to broth.
Add onions and remaining ingredients to broth; cover and cook over low heat, stirring occasionally, 2 hours.