1. Preheat the oven to 475°. In a small bowl, combine 2 teaspoons of the mustard with 2 teaspoons of the olive oil and the thyme. Season the chicken breasts with salt and pepper, then brush them all over with the mustard mixture. Pat 2 tablespoons of the Parmesan all over each breast. Transfer the chicken breasts to a rimmed baking sheet. Bake the chicken on the top shelf of the oven for about 15 minutes, or until just cooked through and nicely browned.
2. Meanwhile, in a medium bowl, combine the remaining 1 teaspoon each of mustard and olive oil; stir in 1/2 teaspoon of water. Add the arugula and tomatoes, season with salt and pepper and toss well. Spoon the salad onto plates, top with the chicken and serve.
Notes: One serving 288 calories, 9.4 gm total fat, 3.1 gm saturated fat, 4 gm carb.