Combine beef stock, water, tomato paste, pepper, salt, bay leaf and garlic in a skillet. Cover and simmer for 15 minutes. Taste and adjust seasonings. Add roast beef slices and green pepper slices. Cook, uncovered, for 15 minutes.
While beef is cooking heat bread in a 350 degree oven for a few minutes. Cut loaves of bread into half lengthwise. Dip each piece of bread, cut side down, into pan liquid (omit this step if you like a dry beef sandwich).
Assemble sandwiches dividing beef and peppers evenly between the 4loaves of bread.