In a heavy skillet, heat the oil and saute the onions for 5 minutes. Add the garlic, peppers, tomatoes, spices, and meat and saute for 5 more minutes.
Add the Sherry and simmer, uncovered, 5 minutes. Add the potatoes and enough water to cover the meat and potatoes. Simmer until the potatoes are tender, about 25 minutes. Season with salt and pepper. Serve with white rice.