Heat oven to 375°F. Make pie crusts as directed on box for Two-Crust Pie using 9-inch glass pie plate.
In 12-inch skillet, cook ground beef and onions over medium-high heat, stirring frequently, until beef is thoroughly cooked; drain.
Stir in cheese, dressing and the mustard. Reduce heat to low; cook 2 to 3 minutes, stirring occasionally, until cheese is melted. Spoon beef mixture into crust-lined pie plate. Arrange pickle chips over beef mixture.
Top with second crust; seal edge and flute. Sprinkle with sesame seed. Cut slits in several places in top crust. Cover crust edge with 2- to 3-inch-wide strips of foil to prevent excessive browning; remove foil during last 15 minutes of baking.
Bake 30 to 40 minutes or until crust is golden brown. Let stand 10 minutes before serving. Top pie with lettuce and tomatoes. Serve with ketchup and mustard if desired.