Heat a grill over medium heat. Combine ¾ tsp ground cumin, ¾ tsp smoked paprika, ¾ tsp dried oregano or 1 tbsp chopped fresh, ¾ tsp sea salt, ¼ tsp crushed red pepper flakes and salt together in a small bowl. Slice 2 limes very thinly into rounds. Skewer 1 ½ pounds boneless, skinless halibut or other firm white fish, cut into 1-inch pieces and lime slices on double-pronged or 2 parallel skewers, beginning and ending with the halibut. Brush halibut with olive oil and sprinkle both sides with reserved spice mixture. Brush grill with olive oil and grill skewers 2 ½ to 4 minutes on each side, depending on thickness, until fish flakes easily with a fork. Cut additional limes into wedges and serve with skewers. NOTE: you can also thread cherry tomatoes or super thin ribbons of zucchini with the fish and lime.