1. Preheat oven to 375°.
2. Cook pasta according to package directions, omitting salt and fat. Drain well; place in a large bowl.
3. Melt 1 tablespoon butter in a large saucepan over medium-high heat. Add bell pepper; sauté 5 minutes or until tender. Add to pasta.
4. Add flour to pan. Gradually add milk, stirring with a whisk until smooth. Bring to a boil; cook 2 minutes or until thickened, stirring constantly. Remove from heat. Add cheeses, stirring until cheeses melt and mixture is smooth. Stir in jalapeño and salt. Add cheese mixture to pasta, tossing well to coat. Stir in green onions. Spoon pasta mixture into a 13 x 9–inch baking dish coated with cooking spray.
5. Place bread slices in a food processor; pulse 10 times or until coarse crumbs measure about 1 cup. Melt remaining 1 tablespoon butter. Combine butter and breadcrumbs in a small bowl; toss until blended. Sprinkle breadcrumb mixture over pasta mixture. Bake at 375° for 15 minutes or until browned.