Preheat the oven to 350°F, and then line an 8x8-inch baking pan with parchment paper, leaving a little bit of an overhang.
Place the oats, pistachios, and walnuts into a blender or food processor and pulse until broken down (note: they do not have to be a fine powder – in fact, a little chunk gives more texture).
In a medium bowl, combine the wet ingredients, including the melted coconut oil, peanut butter, brown sugar, honey, eggs, applesauce, and vanilla.
In a separate bowl (or using the blender pitcher or food processor bowl to save a dish), combine the dry ingredients, including the rolled oats, salt, baking soda, pistachios, walnuts, coconut, sesame seeds, and cranberries.
Transfer the dry ingredients to the wet ingredients stir to combine.
Bake for 20-25 minutes.
While the cake is baking, make the coconut whipped cream frosting: scoop the cream from the top of the cans of coconut milk, leaving the water behind, and place the cream in a mixing bowl. Add the honey and vanilla extract, and using either a stand mixer or hand mixer, mix on high speed until the cream is smooth, forms soft peaks, and is slightly increased in volume. Chill until ready to frost.
Let the oatmeal cake cool for 5-10 minutes in the pan, and then remove it and place it on a cooling rack.
Frost, slice, and enjoy!