To prepare filling, combine pimiento and next 5 ingredients (through egg); set aside.
To prepare beef, cut a 2 1/2-inch-wide horizontal slit into the end of the roast, and cut through to the other end to form a deep pocket using a long, thin knife. Spoon filling into pocket, and pack using the handle of a wooden spoon (the roast will be very full). Secure open end of roast with twine 1/2 inch from edge. Combine salt, cumin, thyme, pepper, and garlic; rub over the roast.
Heat oil in a 6-quart Dutch oven over medium-high heat. Add roast to pan; cook 5 minutes, browning on all sides. Add 2 cups water and remaining ingredients to pan; reduce heat to medium-low. Cover and cook 2 hours or until roast is tender, turning roast after 1 hour.
Transfer meat to a cutting board or work surface. Using a slotted spoon, transfer potatoes to a platter; keep warm. Simmer liquid in pan until reduced to 1 cup (about 15 minutes). Discard bay leaf.
Remove twine before cutting roast into 12 slices.