In the bowl of a mixer, cream coconut oil with sugars until creamy. Add eggs and vanilla and beat until combined. Add flour, baking powder, baking soda, and salt and mix until combined. Add oats, Rice Krispies, and chocolate chips.
Add water if needed if dough seems dry. Coconut oil is drier than margarine or oil, so recipes using it tend to need a little more moisture.
Using a round tablespoon measuring spoon, scoop tablespoon sized scoops of cookie dough onto a parchment lined baking sheet. Bake for 10 minutes, or until edges are golden. Let cool.
Once all cookies are baked and cooled, spread marshmallows on a parchment lined baking sheet. Bake for 6-7 minutes, until marshmallows are expanded and golden on top. Remove from oven and immediately use marshmallows to sandwich two cookies together.
If making ahead, freeze in an airtight container with parchment paper between the layers.