Place cookies in a food storage bag and crush them with a rolling pin until coarse crumbs. Place in a bowl and combine with olive oil.
Season the salmon on both sides lightly with salt and pepper. Place skin side down on a work surface and spread the top with mustard. Divide the cookie mixture between the salmon tops and press down.
Heat vegetable oil in a 12-inch cast iron skillet over medium-high heat until hot then add the salmon skin side down. Cook for 3 minutes or until the skin is crispy. Transfer to the oven and cook for another 5-8 minutes depending on the size, or until the salmon is done.