In the meantime, make the burger sauce by stirring all of the sauce ingredients together until combined. Set aside.
If desired, toast the buns directly on the grill, for about 1 minute, until toasted. Remove to a tray.
Season both sides of the beef patties with salt and pepper, then cook on the grill for about 2-3 minutes on each side, until browned on the edges and cooked through to your desired doneness.
Place one slice of cheese on each patty just before removing from the grill, to melt slightly. Remove the beef from the grill, then allow to rest for a couple minutes.
To assemble the burgers, place a leaf of lettuce on the bottom bun to prevent the bun from getting soggy. Then place two cheese beef patties on top, then the tomato, red onion, and pickles. Spread the inside of the top bun with a tablespoon or more of burger sauce, then place on top of the burgers. Enjoy!
Storing leftovers: Place the cooled burger patties in an airtight container in the fridge for up to 4 days. Or, you can freeze them for up to 2 months. Store all sauces and other ingredients separately.To reheat: I microwave the burger patties at 50% power for about 2 minutes, until they are just warmed through. This time will vary depending on your microwave, so be very careful not to overcook them or they'll get tough and musty. You can also reheat them in a covered skillet over medium heat for about 8-10 minutes.If the patties are frozen, I recommend letting them thaw first. Ideally, move them from the freezer to the fridge the night before.