On a large plate, mix together breadcrumbs, Parmesan, zest, 1/2 teaspoon salt and 1/2 teaspoon pepper. Set aside.
Butterfly chicken and gently pound to 1/4 thick and even. Place in a bowl and add mustard and mayo and toss until fully coated. Dredge in breadcrumb mixture, gently pressing down to adhere breadcrumbs.
In a skillet on medium-high heat, add oil. When hot, add chicken and fry for 1 to 3 minutes on each side. Remove to a towel-lined plate.
In a small bowl, add arugula, tomatoes, lemon juice and 1/2 teaspoon salt. Toss. Plate chicken, top with arugula mixture and shaved Parmesan.