Score your spaghetti squash with a knife and place it into your Instant Pot. Add 1 cup of water. Pressure cook on high for 13-15 minutes depending on the size of your squash. If your squash is too large for your Instant Pot, you can cut it in half along the equator and put it in your Instant Pot with 1 cup of water, and cook for the same amount of time.
While your squash is cooking, brown your spicy sausage in a pan with 1 tablespoon olive oil. Once it is browned, add your red onion and white onion to the same pan and saute for 5 minutes.
Preheat your oven to 400 degrees. At this point, your spaghetti squash should also be finished. Manually release the pressure and be very careful getting the squash out-it will be HOT. I let it cool for a few minutes before cutting it in half. Once I can, I cut it in half (I like to do it on the equator) then remove the seeds with a spoon. Next, use a fork to scrape out the meat of the squash and place it in a mixing bowl.
Next is to add all of the sauce ingredients to a blender and mix it until it is creamy.
Combine the sauce, meat, and veggies into the bowl with the spaghetti squash. Mix until everything is coated then move the ingredients to a casserole dish. Cook in the oven for 20 minutes or until the top is golden brown.
If you like the top a little bit crispy, like me, broil the casserole for 2-3 minutes. Serve and enjoy!