Preheat the oven to 375ºF. Toss the butternut squash with the olive oil on a baking sheet. Season to taste with salt and pepper. Roast for 25-30 minutes, until tender and brown in spots.

Meanwhile, grease an 8×8-inch baking dish with olive oil. Set aside.

In a large skillet over medium heat, cook the sausage, crumbling it up with a wooden spoon, for 3-5 minutes. Add the onion. Cook, stirring occasionally, until the sausage is cooked through and the vegetables are just tender, about 5 minutes. Remove from heat.

Arrange the roasted squash in the bottom of the greased baking dish. Add the sausage and onions, spreading them out evenly. In a large bowl, whisk together the eggs, water, and a generous pinch each of salt and pepper. Pour the egg mixture over the sausage and vegetables.

Bake for 35-40 minutes, until puffed and cooked through.