Preheat grill to 350° to 400° (medium-high) heat. Combine first 5 ingredients gently. Stir onion and mango chutney into meat mixture. Shape mixture into 6 (5-inch) patties.
Grill, covered with grill lid, 6 to 7 minutes on each side or until a meat thermometer inserted into thickest portion registers 170°. Serve on Homemade Hamburger Buns. Top each burger with a small wedge of blue cheese, arugula, whole grain Dijon mustard, and Red Onion Relish.