If using Spam, thinly slice and pan fry for a minute or two on each side over medium heat. If using leftover cooked meat, you can heat it in the microwave as necessary. If using canned tuna, press the liquid out.
Clean and pat dry the vegetables with a paper/kitchen towel. Thinly slice, shave (with a peeler), or julienne the cucumber or carrot. You can lightly sauté the cucumber or carrot, but not necessary.
Put a sheet of nori, shiny side down and shorter side towards you (the photo may not look like that because of the camera angle), on a cutting board or plate. Cut a slit to the middle of gim from the short side.
Lift the bottom left quarter and fold it onto the top left quarter, then to the top right, and finally to the bottom right. Press lightly and tuck the filling in after each fold.