For the chicken: Preheat the oven to 400 degrees F.
Place the chicken, breast-side up, in the center of a roasting pan (see Cook's Note). Sprinkle liberally with salt and roast, undisturbed, 25 minutes. Remove and let the par-cooked chicken rest (the breast skin should be nicely browned).
For the crust: Place the breadcrumbs on a baking sheet and toast in the oven for 5 minutes. Remove and set aside. Finely chop the arugula and place in a medium bowl along with the toasted breadcrumbs. Place the peppercorns on a flat surface such as a cutting board and, using the underside of a skillet, crack them. (The peppercorns should be very coarsely crushed.) Add the peppercorns and butter to the bowl with the breadcrumbs and arugula and mix well.
Gently pat the crust on top of the chicken breast. Place the chicken back in the oven and roast until the juices run clear or a thermometer inserted in the thickest part of the thigh (avoiding bone) registers 160 to 165 degrees F, an additional 25 to 35 minutes (see Cook's Note). Let rest at least 10 minutes, then carve and serve.
I like to use a baking sheet with a fitted rack or a shallow roasting pan. Anything with low "walls" will allow for maximum browning of the skin.
For cook time, I count 12 to 15 minutes per pound of bird.