Here’s a little trick: Thread salmon pieces onto two skewers so they don’t flip and spin every time you turn them on the grill.
Prepare grill for medium heat. Mix oregano, sesame seeds, cumin, salt, and red pepper flakes in a small bowl to combine; set spice mixture aside.
Beginning and ending with salmon, thread salmon and folded lemon slices onto 8 pairs of parallel skewers to make 8 kebabs total. Brush with oil and season with reserved spice mixture.
Grill, turning occasionally, until fish is opaque throughout, 5-8 minutes.