Taken from Napoleon's Everyday Gourmet Plank Grilling
That’s right people; I even plank SPAM—I told you, you can plank anything! Quick fact: The wonderful state of Hawaii sells more SPAM than anywhere else in the USA.
Preheat grill to medium heat. Open tin of SPAM, tip if upside down and give it a good shake to loosen from the tin. Slice SPAM in half. Place both halves on plank. Place plank on grill and close lid. Plank bake for 15 to 20 minutes until the SPAM is a little crisp on the outside and heated through.
Meanwhile, in a small bowl, combine the red onion, green olives, gherkins and honey mustard; set aside. Remove SPAM from grill. Slice each half of the planked SPAM into 8 slices. Brush the bottom half of each bun with mayonnaise. Top each half with shredded lettuce and 4 slices of tomato. Arrange the planked SPAM slices on top of the tomatoes. Spoon the red onion mixture evenly over top of each sandwich. Top with bun lid and serve immediately.