Lightly grease a 9-by-13-inch baking pan with coconut oil. In a large pot, melt the 3 tablespoons of coconut oil. Add the marshmallows and cook thoroughly over low heat, stirring constantly, until they are melted, about 5 minutes. Add the creamy peanut butter and stir until incorporated. Remove the pot from the heat and immediately add the Rice Krispies. Using a wooden spoon or firm spatula, stir to coat them completely. Scrape the mixture into the prepared baking pan and, using a sheet of wax paper, press evenly on the mixture to compact it. Let the Rice Krispie treats cool completely, then cut them into squares and serve.