1. Sauté onions in oil in medium skillet on medium heat 8 to 10 minutes or until onions are light golden brown in color. Remove from heat; set aside.
2. Spread one side of each slice of bread with 1/2 Tbsp. of the butter. Top 4 slices evenly with ham and cheese. Place on oven-proof plate under heated salamander or broiler 1 to 2 minutes or until ham is heated and cheese is melted.
3. Top evenly with cooked onions and arugula. Cover with second slice of bread. Cut in half and serve.
Nutritional information per serving: Calories 725; Total Fat 27g; Saturated Fat 14g;
Trans Fat 0; Cholesterol 92mg; Sodium 2196mg; Total Carbohydrate 79g; Dietary Fiber 4g;