Grease an 8" x 8" baking dish with 1 tbsp cooking fat of choice.
Preheat the oven to 400° F. Cut the spaghetti squash in half along the length and place cut side down on a baking sheet. Bake at 400° F for 30-35 minutes, until the skin gives when you press a finger to it. Remove from oven and let cool until cool enough to handle. Reduce oven temperature to 350° F.
While the spaghetti squash bakes, brown the bacon. Saute the lardons in a large cast iron skillet or in your Instant Pot, stirring occasionally, until browned and cooked through. Once crisp, use a slotted spoon to remove the bacon to a paper towel lined plate. Reserve 2 tbsp of bacon fat.
Make the Carbonara sauce: in a food processor or blender, combine the cashews, egg yolks, nutritional yeast, bacon fat, water, sea salt, and black pepper. Blend/pulse until smooth and combined completely. Dump the sauce into a large bowl and add the peas and bacon bits.
Use a fork to remove and discard the seeds and slimy part of the spaghetti squash halves. Remove the spaghetti squash threads with the fork and add to the bowl with the sauce, bacon, and peas. Use tongs to toss and combine completely. Spoon the spaghetti squash mixture into the greased baking dish and smooth out the top.
Bake the casserole at 350° F for 25-30 minutes until the casserole starts to brown around the edges and dries on the top. Cut into slices, plate, serve hot, and enjoy!
