Season the chicken inside and out with salt and pepper. Truss it and brush with olive oil. Place on a rack in a roasting pan and roast until browned but only about half-cooked, 40 minutes.
Meanwhile, in a small bowl, combine the ΒΌ cup black pepper, a pinch of salt, and the mustard and stir well. Drizzle in olive oil, whisking until blended.
Remove the browned chicken from the oven and brush with the black pepper and mustard mixture. Return to the oven and continue roasting until the juices run clear when a thigh is pricked, about another 30 minutes. Let rest for 10 minutes.
While the chicken rests, in a medium bowl, combine the parsley, red onion, cherry tomatoes, the olive oil, the red wine vinegar, and salt and pepper to taste and toss well.
Carve the chicken and arrange on serving plates. Drizzle with the pan juices and the spicy oil, top with the parsley salad, and serve immediately.