In a large skillet, cook the beef and onion over medium heat until meat is no longer pink; drain. Stir in the Worcestershire sauce, salt and pepper.
Place half of the potatoes in a greased 13-in. x 9-in. baking dish; layer with meat mixture, peas and remaining potatoes. Set aside.
In a large saucepan, melt butter over medium heat. Stir in the flour, salt and pepper until smooth. Gradually stir in milk. Bring to a boil; cook and stir for 2 minutes or until thickened. Stir in cheese until melted. Pour over potatoes.
Cover and bake at 350° for 1-1/2 hours or until potatoes are tender.