Preheat oven to 375 F. From lemons, grate 1 teaspoon peel and squeeze 3 tablespoons juice. Set aside. Spray 9-inch glass or ceramic pie plate with nonstick cooking spray.
In medium bowl, stir lemon peel, ricotta, 1/2 teaspoon salt and 1/4 teaspoon freshly ground black pepper until blended. Spread ricotta mixture evenly in prepared pie plate. Bake 1 hour or until cheese is lightly browned. Let stand 10 minutes to allow cheese to set. Slice into 12 wedges.
Meanwhile, in medium bowl, whisk together lemon juice, Dijon, 1/4 teaspoon salt and 1/8 teaspoon freshly ground black pepper. Whisk in olive oil in slow, steady stream until blended. Stir in chopped tomatoes.
To serve, place 1 ricotta wedge along with some greens on each of 12 serving plates. Top greens and ricotta with tomato vinaigrette.
