In a measuring cup with a spout, mix the melted coconut oil, honey, egg and vanilla to combine. With the processor running, pour the egg mixture in, processing until just combined. Pour over par-baked crust. Arrange rhubarb on top. Bake for 40 minutes or so in pre-heated oven. You are probably going to have to cover the pan with foil if the top is browning too fast. Wait until it cools, slice and serve.