Make the sauce: Place all the sauce ingredients in a food processor bowl, puree until smooth and thick, season with salt to taste, set aside.
Heat 1 tablespoon of frying oil on a grill pan / regular frying pan over medium heat.
Slice the halloumi into ¼ inch (¾ cm) slices. Grill the slices for a few minutes on both sides until lightly browned on the outside and warm and soft through the middle. Transfer to a plate.
Peel the pineapple, cut into ½ inch (1 cm) slices, cut out the tough core (I like to use an apple corer for that). Grill the slices for a few minutes on both sides until lightly browned and softened. Transfer to a plate.
Grill the sliced hamburger buns very briefly (about 30 seconds) until lightly browned. Transfer to a plate.
Prepare the avocado: cut the avocado in half, remove the pit, and scoop out the flesh. Mash with a fork, mix with the lime juice, season with chili flakes (optional), and salt and black pepper to taste.
Assemble: spread avocado mixture on one half of each bun, top with halloumi slices, then pineapple slices, spoon over the sauce, place the lettuce leaves on top, cover with the other half of the bun.
Enjoy!