Mediterranean Meatball Sandwiches

In a large bowl, combine onion, parsley, salt and pepper. Add beef; mix lightly but thoroughly. Shape into four 4x2-in. oblong patties., Grill patties, covered, over medium heat or broil 4 in. from heat 4-6 minutes on each side or until a thermometer reads 160°. Serve on pitas with tzatziki sauce and toppings as desired.