Pre heat your oven to 400 degrees and line a large baking sheet with tinfoil or parchment paper.
Rub the oil on the insides of the squashes and sprinkle with salt. Roast, cut-side down, until fork tender, about 40 minutes to 1 hour. Set aside to cool.
Once cool, bring a medium pot of salted water to a boil. Once boiling, add in the chicken and cook until no longer pink inside, about 12-16 minutes. Set aside to cool.
In a large frying pan with high sides, heat up the olive oil on medium/high heat. Add in the onion and celery and cook, stirring frequently, until they begin to soften, about 3-4 minutes.
Add in 1 cup of each milk (reserving the rest for later) along with salt, garlic/onion powder, parsley and pepper. Stir until well mixed and bring to a boil. While you wait for it to boil, whisk the tapioca starch and the remaining 1 Tbsp of each milk together in a small bowl until smooth and lump-free.
One boiling, pour the tapioca starch mixture in (while constantly whisking so it doesn't clump up!) and boil for 3-4 minutes, whisking CONSTANTLY, until it really begins to thicken.
Reduce the heat to medium and simmer, whisking frequently, until very thick - just a little thinner than condensed soup - about 10-12 minutes.
Heat your oven to 350 degrees. Scrape the spaghetti squash into a large kitchen towel. You should end up with about 8 packed cups (or 1100g) of spaghetti squash and I do recommend measuring to make sure!
Wrap the squash in the kitchen towel and ring out as much moisture as you can. Place into a large bowl.
Shred the chicken (you should have about 2 very packed cups or 290g) and add it into the bowl along with the remaining 1/2 tsp of salt.
Add in the homemade soup and stir everything together until well mixed- I find it a lot easier to use your hands here, even though it is messy!
Once mixed, press down firmly into a large baking dish and cover with the crackers, lightly pressing them into the top of the casserole.
Bake until the casserole is bubbly, about 45 minutes.
Let stand for 10-15 minutes to cool and then garnish with parsley and DEVOUR
*I use my small food processor so dicing all that onion is quick and easy