Spray a 9 by 13 inch pan generously with cooking spray.
In a large soup pot, melt the butter over medium low heat. Once melted, add the marshmallows, stirring in the butter. Stir occasionally. Once melted, remove from the heat.
Add the lemon zest and lemon juice to the marshmallows and stir until combined. Add the lemon cookies and Rice Krispies Cereal and coat them with the marshmallows. Pour into the pan and press down with a cooking spray coated spatula.
While the Rice Krispie Treats are cooling, melt the white chocolate chips according to directions. Once melted stir in the vegetable oil to thin the chocolate. Using a fork, drizzle the chocolate over the Rice Krispies Treats. Allow the chocolate to harden and then cut into square pieces. Best if served the same day.