Place a chicken breast between 2 layers of plastic wrap, and using a meat mallet, pound to a 1/4-inch thickness. Repeat with remaining chicken. Brush both sides of chicken with olive oil, and season with salt and pepper.
Preheat a stovetop grill pan over high heat until very hot. Cook chicken until grill marks appear, about 3 minutes. Turn, and continue cooking until browned and cooked through, 2 to 3 minutes more. If cooking in batches, remove from heat and keep warm until serving.
Squeeze lemon juice over each chicken breast. Serve warm, topped with herb salad and sauteed radishes.