Dice the cucumber, cut two slices of tomato, and two slices of red onion.

In a medium bowl, combine together the ground beef, brown sugar, and salt.

Split the ground beef in half and form two round flat burgers.

On a grill or in a medium skillet over medium heat, cook the burgers for about 5 or 6 minutes on each side for medium done.

In a small bowl combine the sour cream, mayonnaise, salad dressing, and cucumber.

Place the bottom half of each hamburger bun on a plate. Add the lettuce, feta cheese, burger patty, cucumber sauce, tomato slice, red onion slice and top with the other half of the bun.