These Greek beef burger patties are filled with Mediterranean flavors like lemon, roasted red peppers, garlic, and more! The burgers are then topped with a smear of tzatziki, as well as thinly sliced cucumbers, red onion, and lettuce. These burgers are the perfect weeknight meal because they cook in under 10 minutes on the grill.
Add ground beef, onion, roasted red bell pepper, garlic, lemon peel, lemon juice, oregano, and red pepper flakes to a large bowl. Mix everything with your hands until combined.
Divide the ground beef mixture into six 5-ounce patties. Add 1 ounce of feta cheese to the middle of each patty. Fold the patty around the cheese, then flatten patties to ¾ inch thick. Make a depression in the center of the patties using your thumb to prevent the burgers from puffing up on the grill during the cooking process. Season each side of the patties with salt and pepper, as desired. Place burgers in the refrigerator for 15 minutes to firm up or until ready to cook on the grill.
Cook burgers covered over direct heat for 3-5 minutes on each side, or until they reach an internal temperature of 150°F (medium-well).
To serve, toast hamburger buns. Spread a generous amount of tzatziki sauce on the top and bottom buns. Layer lettuce, a burger patty, sliced cucumbers, onions, and tomato on the bottom bun. Top with the remaining half of the bun and serve immediately.
Burger patties can be made 1 day ahead of time and stored in the refrigerator until you're ready to grill. Avoid seasoning the outside of the burgers with salt and pepper ahead of time. Season right before grilling.