In 12-inch nonstick skillet, cook sausage and onion over medium heat 5 to 7 minutes, stirring occasionally, until some pink remains. Stir in mushrooms and bell pepper; continue cooking until sausage is no longer pink. Add milk, hot water and sauce mix (from Hamburger Helper™ box); stir to combine. Stir in uncooked pasta (from Hamburger Helper™ box). Heat to boiling, stirring occasionally. Reduce heat; cover and simmer 9 to 11 minutes, stirring occasionally, until pasta is tender and sauce is thick. Stir in vinegar.