Cook the pasta in lightly salted water in conjunction with the package instructions until not quite al dente and still quite chewy. Drain and set aside, reserving 3 cups of the pasta water.
Place a large saucepan over high heat and add 2 tablespoons butter. Add the chicken and cook until browned and almost cooked through, about 5 minutes.
Meanwhile, place a skillet over medium heat and add the remaining 2 tablespoons butter. When the butter has melted, add the panko and 1/2 teaspoon dried parsley. Season with salt and pepper, then toss and cook until golden brown, about 3 minutes.
Add the bell pepper and onion to the pan with the chicken and cook until they have slightly softened, about a minute, then add the pimientos and stir. Reduce the heat to medium-low and add the cream of mushroom soup, pasta water and milk, then bring to a simmer. Add the Worcestershire sauce, remaining 2 teaspoons dried parsley, cayenne and seasoned salt to taste, followed by the cheeses, a handful at a time. Stir until completely incorporated. Add the frozen peas followed by the cooked pasta, then stir and cook until the pasta is perfectly cooked, a couple of minutes. Add salt and pepper, stir again, then sprinkle the toasted parsley breadcrumbs over the top.