Slice a lemon and a lime into very thin slices. On your pre-soaked skewers alternate salmon, citrus slice, scallop, repeating until your skewer is full. Do this until you have skewered all of your scallops and salmon. Sprinkle lightly with cajun seasoning and return to the refrigerator until ready to cook.
Once your grill is ready, place the soaked cedar plank onto the grill and close the lid for three minutes. Flip the planks, add your prepared kabob skewers, and close the lid. You want to cook the skewers approximately 15 minutes and then check for doneness. Don’t overcook the scallops!
You do not need to flip, turn, rotate or disturb your skewers in any way while they cook. You want to check occasionally for flareups but if your boards were properly soaked this should be a pretty hands-off operation. You may see some smoldering of the boards around the edges and you will probably here that familiar POP of a campfire from time to time. If you see flames you can spritz the boards with a little water. Otherwise, leave it be!
When your kabobs are done remove them, while still on the planks, with tongs and a pot holder. Place the cedar planks on a heatproof surface for serving. Just before you invite your guests to dig in brush each of the skewers with the Cajun Citrus Butter. Provide additional Cajun Citrus Butter for dipping.