In a medium bowl, combine first 5 ingredients (ground beef through tomatoes) and 2 tablespoons of the Greek seasoning; blend lightly but thoroughly then shape into 6 oval 1/2-inch thick patties.
Heat a large non-stick skillet over medium heat until hot; add beef patties and cook for 7 to 8 minutes or until no longer pink in the center and juices run clear, turning once.
Meanwhile, in a small bowl, prepare Mediterranean Mayo: combine mayo, remaining Greek seasoning, mustard and lemon juice; blend well then set aside.
Place a burger on the bottom half of each bun then layer with 1 tablespoon of Mediterranean Mayo, desired topping(s) and the top half of the bun.