Combine lemon rind, juice, oil, and garlic in a large bowl. Sprinkle with 1/4 teaspoon salt and 1/4 teaspoon pepper.
When ready to serve add arugula and toss well, making sure to coat leaves evenly.
Place each chicken breast half between 2 sheets of heavy-duty plastic wrap; pound each piece to 1/4-inch thickness using a meat mallet or small heavy skillet. Sprinkle both sides of chicken with remaining 1/4 teaspoon salt and remaining 1/4 teaspoon pepper. You can do this earlier in the day and cover and refrigerrate if needed.
Heat a grill pan or a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add chicken, and cook for 4 minutes on each side or until done. Remove chicken from pan, and keep warm.
On a plate, place one chicken breast top with a heaping of salad and top with a handful of tomatoes.