Melt the butter in a medium skillet over medium heat. Add the onion; cook for 5 minutes, stirring occasionally. Add the chopped tomato; cover and simmer for 5 minutes. Uncover; cook for 2 minutes or until mixture is thick, stirring occasionally. Remove from heat; set aside.
Beat eggs in a large bowl. Add the milk, Swiss cheese, 1/2 cup Parmesan cheese, dill weed and salt; mix well. Stir in onion mixture. Pour into pie shell. Top with the sliced tomatoes and the remaining 1 tablespoon parmesan cheese. Bake in a preheated 350 degrees F oven for 55 minutes or until set. Let stand 10 minutes and serve.