Preheat oven to 425 degrees Fahrenheit.
Spiralize butternut squash with the larger noodle blade. (I recommend the OXO Sprializer ).
Place "noodles" on a large cookie sheet, drizzle with olive oil, and lightly season with sea salt and pepper.
Use your hands to spread the oil around the noodles. Bake for 15 minutes, until softened but still slightly underdone.
While the noodles are baking, prepare spaghetti sauce.
Brown sausage in a skillet for about 10 minutes over medium high heat, then remove from pan and slice.
In the same skillet, add olive oil and minced onion. Saute for 5-10 minutes over medium-high heat, until onions are translucent.
Add bell peppers, and continue to cook for another 5 minutes.
Add the tomato basil sauce, olives, and zucchini, and continue to simmer for 10 minutes. Remove from heat and set aside. Resist the urge to "thin" out the sauce- you will want it really thick so you can "slice" the casserole.
In a large baking dish (I used an rounded rectangular 10 x 8 inch baking pan, and this recipe perfectly fills it), begin by layering in 1/2 of the butternut noodles.
On top of the noodles, layer 1/2 of the sausage sauce, followed by 1/2 of the cheese.
Add 1 more layer of noodles, sauce, and cheese.
If baking the dish right away, bake it in the still heated oven for 30 minutes, covered (until the sauce is bubbling). Uncover the dish, and lightly brown the cheese, 5-10 additional minutes.
The dish can also be made ahead and baked up to a day later. If the dish has full cooled prior to baking, preheat oven to 425 degrees Fahrenheit, and bake for 45-55 minutes covered (until sauce is bubbling). Remove the cover, and brown the cheese for an additional 5-10 minutes.
Garnish with parsley, and allow to "set" for 10-15 minutes if you want the slices to come out nicely. When it's very hot, the slices won't hold as well.