Combine mixed peppercorns, salt and red pepper in small bowl. Reserve 1 teaspoon for sauce. Press remaining pepper mixture evenly onto beef steaks. Toss bell peppers and mushrooms with oil to coat in a large bowl; season with salt and pepper, as desired. Thread mushrooms evenly onto two 12-inch metal skewers.
Place steaks in center of grid over medium, ash-covered coals; arrange bell peppers and mushroom kabobs around steaks. Grill steaks, covered, 11 to 16 minutes (over medium heat on preheated gas grill, 15 to 19 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally. Grill bell peppers and mushrooms 12 to 15 minutes or until tender, turning occasionally.
Meanwhile prepare sauce. Melt butter in small saucepan over medium heat. Add onion and garlic; cook and stir 4 to 5 minutes or until tender. Stir in remaining sauce ingredients and reserved 1 teaspoon pepper mixture; bring to a boil. Reduce heat; simmer 3 minutes to blend flavors, stirring occasionally. Place in blender or mini food processor container. Cover; process until puréed.
Remove bones and carve steaks into slices. Serve with sauce.
Nutrition information per serving: 444 Calories; 207 kcal Calories from fat; 23 g Total Fat; 8 g Saturated Fat; 11 g Monounsaturated Fat; 76 mg Cholesterol; 1212 mg Sodium; 28 g Total Carbohydrate; 3.3 g Dietary Fiber; 32 g Protein; 8.1 mg Niacin; 0.7 mg Vitamin B6; 2.5 mcg Vitamin B12; 6 mg Zinc; 16.3 mcg Selenium;