Heat greased grill to medium-high heat.
Mix meat, spinach, bacon, garlic powder and crushed red pepper just until blended; shape into 8 meatballs.
Press 1 VELVEETA cube into center of each meatball, completely enclosing VELVEETA. Flatten to 2-1/2-inch diameter. Grill 5 min. on each side or until done (160ºF).
Fill buns with burgers.