1Spray 12-inch nonstick skillet with cooking spray; heat over medium-high heat. Cook onion in skillet 2 minutes, stirring occasionally, until crisp-tender. Stir in soup and milk. Heat to boiling, stirring constantly. Stir in pasta and frozen broccoli. Heat to boiling; reduce heat to medium. Cover and cook 5 minutes.
2Stir in tuna. Cover and cook about 5 minutes, stirring occasionally, until pasta is tender.
3Mix crackers and cheese; sprinkle over tuna mixture. Cover and let stand 1 to 2 minutes or until cheese is melted.