Mix the quick oats and milk in a large bowl. Cover and refrigerate for at least 30 minutes until the oats have fully absorbed the milk.

Prepare the container: Lightly grease a 7x5 inch glass dish with a little cooking oil.

Prepare the oat mixture: Gently mix the mini marshmallows, coconut flakes, and raisins into the milk-soaked oats. Set aside.

Prepare the white chocolate mixture: In a microwave-safe bowl, add the white chocolate chips. Microwave for 1.5 to 2 minutes. Carefully remove the bowl and stir with a whisk until melted. If not melted, repeat microwaving for 30 seconds, remove, and stir until fully melted. Add the peanut butter and coconut oil, and mix well.

Make the cookie dough: Quickly add the white chocolate mixture to the oat mixture and stir with a spoon until combined. The cookie dough is now ready.

Pour the cookie dough into the greased glass dish and press flat with a spoon.

If using dark chocolate chips, evenly press them into the cookie dough. Press flat again with a spoon.

Cover and refrigerate for at least 2 hours until the white chocolate has set again.

Remove and cut into 12 small squares to serve.

[Note] All measurements are shown using US cups, tablespoons, and teaspoons.