In 10-inch skillet, cook beef and onion over medium-high heat 5 to 7 minutes, stirring frequently, until beef is brown; drain.
Stir in milk, hot water, uncooked pasta and sauce mix (from Hamburger Helper box) and barbecue sauce. Heat to boiling, stirring occasionally.
Reduce heat; cover and simmer about 10 minutes, stirring occasionally, until pasta is tender. Remove from heat; uncover.
Arrange cheese slices over top; place tomato slice and bacon strip on each cheese slice in spoke pattern. Let stand 5 minutes (sauce will thicken as it stands).