Step 1: Set up your grill for indirect grilling and heat to medium-high. Grill the plank directly over one of the burners until charred on one side, 2 to 4 minutes. Remove from the grill and let cool.
Step 2: In a mixing bowl whisk together the mayonnaise, Dijon, and Fennel Pepper Rub.
Step 3: Arrange the salmon, skin side down, on the plank. Spread the mustard mixture on top.
Step 4: Indirect grill the salmon until the glazed is puffed and browned and the fish is cooked through (to about 140 degrees on an instant read meat thermometer), 20 to 30 minutes.