Preheat oven to 450°.
Heat a nonstick skillet over medium-high heat until hot. Add mustard seeds, and cook 1 minute or until seeds begin to pop. Place seeds in a food processor, and process until seeds begin to crack. Add the cilantro leaves and the next 6 ingredients (cilantro leaves through jalapeño); process until finely minced.
Remove and discard giblets and neck from chicken. Rinse chicken under cold water; pat dry. Trim excess fat. Starting at neck cavity, loosen skin from breast and drumsticks by inserting fingers, gently pushing between skin and meat. Spread mustard mixture under loosened skin. Lift wing tips up and over back, and tuck under chicken. Sprinkle the chicken with ground pepper.
Place chicken, breast side up, on a broiler pan. Insert a meat thermometer into meaty part of thigh, making sure not to touch bone. Bake at 450° for 30 minutes. Reduce oven temperature to 400° (do not remove chicken from oven); bake an additional 45 minutes or until thermometer registers 180°. Cover chicken loosely with foil; let stand 10 minutes. Discard skin. Serve with Papaya Mojo, and garnish with cilantro sprigs, if desired.