1Heat oven to 350°F. Spray 2-quart casserole with cooking spray. Cook and drain pasta as directed on package.
2Meanwhile, in 3-quart saucepan, melt butter over low heat. Reserve 1 tablespoon of the butter in small bowl. Stir bell pepper and onions into butter in saucepan. Increase heat to medium; cook and stir 1 minute. Stir in flour, salt, pepper and mustard. Cook, stirring constantly, until mixture is bubbly. Increase heat to medium-high. Gradually add milk, stirring constantly, until mixture boils and thickens, about 5 minutes. Gently stir in bacon and pasta.
3Remove from heat; stir in cheeses until melted. Pour into casserole. Stir bread crumbs into melted butter in small bowl. Sprinkle over pasta mixture.
4Bake uncovered 20 to 25 minutes or until edges are bubbly.