Place red pepper and corn ear into hot oven and roast for 15 minutes or until the skin of red pepper blisters and begins to turn black. Remove the outside skin from the red pepper, remove the seeds, and chop. Remove the corn husk, and remove corn kernels from the ear with a sharp knife.
Meanwhile, prepare the salad dressing by fully combining the mayonnaise, buttermilk, pickle juice, rice vinegar, pasta water, and mustard. The consistency should be fluid but not water-like. If it’s too runny, add more mayonnaise. If the dressing is too thick, add more pasta water.
Boil the pasta according to packaging directions. Drain well. Place pasta in large serving bowl. Toss with 1/4 cup of the salad dressing. Set aside to cool.
Prepare the remaining ingredients. When the pasta has cooled to room temperature, add the remaining ingredients. Toss together. Coat with the remaining salad dressing. Toss well, cover, and refrigerate.