Step 1

Heat oven to 350°F.

Step 2

Cook macaroni as directed on package, omitting salt.

Step 3

Meanwhile, melt butter in large saucepan on medium heat. Add onions; cook and stir 2 min. or until golden brown. Stir in flour; cook 2 min., stirring constantly. Whisk in milk, then dressing. Bring just to simmer, stirring constantly; cook and stir 2 to 3 min. or until thickened. Add cheeses and Sriracha sauce; cook and stir 2 min. or until cheddar is melted.

Step 4

Drain macaroni. Add to prepared cheese sauce along with the bacon; mix lightly.

Step 5

Spoon into in 13x9-inch baking dish sprayed with cooking spray.

Step 6

Bake 20 min. or until heated through.