Create a two-zone indirect fire in grill by banking charcoal on one side. Alternately, light only half the flames of a gas grill set to high.
Place cast iron skillet over direct heat on grill to get hot. Season fish with salt and pepper and set aside.
Toss potatoes with 2 tablespoons vegetable oil in a medium bowl. Season with salt and pepper. Stack 2 large pieces of heavy duty aluminium foil and fold edges up to make a cooking tray for potatoes. Transfer potatoes to foil tray and place on grill over indirect heat. (Add a splash of beer if you’re feeling frisky.) You want to cook the potatoes slowly then move to high heat to get some grill marks. Repeat this same process with corn. Once corn and potatoes are cooked, set aside to cool.
In the meantime, make the Meyer Lemon Vinaigrette. Combine mustard, lemon zest and juice, and salt and pepper to taste. Whisking constantly, slowly add ½ cup vegetable oil and ¼ cup olive oil. Keep whisking vigorously until emulsified.
To cook fish, add ½ cup vegetable oil to hot skillet and wait until oil just begins to smoke. Carefully place snapper in skillet, skin side down. You are looking to get the skin crispy. Cook, skin side down, for about 2 minutes. Turn fish over and transfer skillet to indirect heat zone. The skillet will continue to cook the flesh side of the fish.
Remove corn kernels from cobs and slice charred potatoes. Transfer to a large bowl and add arugula. Season with salt and pepper and drizzle with Meyer Lemon Vinaigrette until everything is evenly coated.
To serve, transfer salad to serving dish and place snapper on top.