Chocolate-Chip, Oat, and Coconut Skillet Cookie

Ingredients: 1/2 cup unsalted butter, softened 1/2 cup brown sugar 1/4 cup granulated sugar 1 large egg 1 teaspoon vanilla extract 1 cup all-purpose flour 1/2 teaspoon baking soda 1/4 teaspoon salt 1/2 cup rolled oats 1/2 cup shredded coconut