Preheat grill for medium heat and lightly oil the grate.
Thoroughly mix ground lamb, rosemary, thyme, garlic powder, salt, and pepper together in a bowl; shape into 4 patties.
Cook the burgers until they are beginning to firm and are hot and slightly pink in the center, about 5 minutes per side. An instant-read thermometer inserted into the center should read 140 degrees F (60 degrees C). Alternately, you can cook the burgers to your desired degree of doneness. Rest burgers while assembling toppings.
Mix mayonnaise and mustard together in a small bowl; spread 1 tablespoon of the mixture onto one side of each bun. Put a burger onto each bun and top with tomato and greens. Sandwich with remaining bun half to serve.
Tips & Tricks
Roasted Rack of Lamb
An amazing roast rack of lamb encrusted with mustard and seasoned bread crumbs.
How to Make Roast Leg of Lamb
See how to season and roast a juicy, tender leg of lamb.