Bring a large pot of water to a boil. Preheat a pizza oven or regular oven to 350 degrees F.
Carefully cut the acorn squash in half, not just by simply slicing through, but by cutting it into a flower shape--as if you were decorating for Halloween. In other words, create jagged edges by making 45 degree slices that connect all around the circumference of the acorn squash. Scoop out the seeds from both sides of the squash.
Add the cleaned, “flower” acorn squash halves to the boiling water and blanch to slightly soften, about 10 minutes. Remove from the boiling water and let cool to the touch.
Meanwhile, gently mix together the crab, mayonnaise, egg yolk, Dijon mustard, fish sauce and chives in a medium bowl. Season with salt and pepper.
Divide the crab mixture between the 2 halves of the squash and place in a 9-by-13-inch or oval baking dish. Bake, rotating the pan halfway through cooking, until everything is golden brown, about 30 minutes. Garnish with fresh dill before serving.