Heat oven to 375°F.

Cut tops off peppers; discard tops.

Remove seeds and membranes; discard.

Place bell peppers on ungreased cookie sheet.

In 10-inch nonstick skillet, cook beef over medium-high heat, stirring frequently, until browned; drain.

Stir in milk, hot water, sauce mix and uncooked pasta (from Hamburger Helper box).

Heat to boiling, stirring occasionally.

Reduce heat.

Cover; simmer 6 to 8 minutes, stirring occasionally, until pasta is tender.

Remove from heat.

Spoon mixture into peppers.

Top each with 1 tablespoon cheese.

Bake 15 to 20 minutes or until peppers are tender and cheese is melted.

Sprinkle with red pepper flakes before serving.