Cover tomatoes with boiling water; let stand 10 minutes or until softened. Drain tomatoes and cut into thin strips. Toss tomato pieces with shredded cabbage and carrot mixture.
In a small mixing bowl combine mayonnaise dressing or salad dressing, milk, mustard, and caraway seed. Add to cabbage-tomato mixture; toss to coat. To assemble sandwiches, place one-fourth of the roast beef and one-fourth of the cabbage mixture in each pita half. Makes 4 servings.