Form the minced meat into 4 flat patties, each about the width of a sesame bun. Season with salt. Heat sunflower oil in a frying pan over medium-high heat. Fry each patty for 5-6 minutes per side until the internal temperature reaches 71°C (160°F).
Cut each sesame bun in half. Toast the inside of each bun half in the frying pan over medium heat for 1-2 minutes until lightly golden.
Mix the mayonnaise, ketchup, and mustard together in a small bowl.
On each bottom bun half, layer in order: lettuce leaf, cooked patty, a couple of slices of cheese, a tomato slice, a ring of onion, and a couple of slices of pickled cucumber.
Spread the mayo-ketchup-mustard mixture on the inside of the top bun half and place it on top of each burger.