Spray bottom of 6-quart slow cooker with cooking spray. Line side of slow cooker with foil; spray foil with cooking spray. Cook and drain macaroni as directed on package, using minimum cook time.
Meanwhile, in 12-inch nonstick skillet, cook beef over medium heat 8 to 10 minutes, stirring occasionally, until thoroughly cooked; drain. Add taco seasoning mix and water; simmer 2 to 3 minutes or until most of liquid is absorbed.
In large bowl, mix cheese sauce, milk and green chiles. Stir in macaroni and beef mixture. Spoon into slow cooker.
Cover; cook on Low heat setting 2 hours. Stir; sprinkle with cheese. Cover; let stand 15 minutes or until cheese is melted. Garnish with jalapeños.