In a large bowl, combine the asparagus, red pepper, onion, oil, salt and pepper. Transfer to a greased 15x10x1-in. baking pan. Bake at 450° for 10-15 minutes or until golden brown, stirring once., Meanwhile, cook pasta according to package directions. In a large saucepan, melt butter over medium heat. Stir in the flour, garlic and pepper flakes until blended. Whisk in broth until blended. Bring to a boil over medium-high heat; cook and stir for 2 minutes or until thickened and bubbly. , Reduce heat. Stir in the cheese, sour cream, lemon juice and zest; heat through. Drain pasta and place in a large bowl. Add cheese sauce and asparagus mixture; toss to coat. Sprinkle with pistachios, basil and additional cheese.