In a medium sized bowl, combine the Greek yogurt, cilantro, & 2 teaspoons minced garlic. Set aside.
In a large bowl, combine the ground beef, 2 teaspoons of the minced garlic, chili powder, & Worcestershire sauce. Form into patties. Sprinkle with salt & pepper to taste. Grill on medium heat for about 8 minutes on each side – or until desired doneness.
Drizzle the sandwich thins with a little olive oil & grill on each side for a couple of minutes. (This step is optional)
Spread a tablespoon of the yogurt sauce on the inside of the bottom bun. Top with a tomato slice & the burger. Spread another tablespoon of sauce on the top half of the bun, and top the burger with it. Serve with additional chopped cilantro to garnish, if desired.