Beef Fajita Salad with Mango-Serrano Vinaigrette

For the Salad: Brush mangos with oil. Place mangos and poblanos on grid over medium, ash-covered coals. Grill poblanos, uncovered, 9 to 10 minutes (gas grill times remain the same) or until skins are blackened, turning occasionally. Grill mangos 8 to 14 minutes (gas grill times remain the same) or until very tender, turning occasionally. Seal peppers in food-safe bag. Let stand 15 minutes. Press black pepper onto beef steak. Brush onion with oil. Place steak on grid; arrange onion around steak. Grill, uncovered, 17 to 21 minutes (over medium heat on preheated gas grill, covered, 13 to 16 minutes) or until steak is medium rare (145°F) to medium (160°F) doneness and onion is tender, turning occasionally. For the Vinaigrette: Cut mangos into 3/4-inch pieces. Combine 1/2 cup mango, lime juice, water and serranos in food processor. Cover; process until smooth. With motor running, slowly add oil, processing until well blended. Season with salt, as desired. To Assemble: Discard skins, stems and seeds from poblanos; cut into 3/4-inch pieces. Carve steak into slices. Halve onion slices. Place beef, remaining mango, onion, poblanos and radishes on platter. Season with salt. Drizzle with vinaigrette; toss to coat. Sprinkle with cilantro