Preheat oven to 375°. Unroll crescent dough and separate into triangles. On an ungreased 12-in. pizza pan, arrange triangles in a ring with points toward the outside and wide ends overlapping. Press overlapping dough to seal.
In a large skillet, cook beef over medium heat until no longer pink, 6-8 minutes, breaking into crumbles; drain. Stir in ketchup and mustard. Remove from the heat.
Spoon beef mixture across wide end of triangles. Top with cheese and pickles. Fold pointed end of triangles over filling, tucking points under to form a ring (filling will be visible). Bake 25-30 minutes or until golden brown. If desired, serve with Thousand Island dressing.