preheat the oven to 400 °F. Grease a 9 x 13-inch glass baking pan.
Spread the bacon out on a large sheet pan. Bake for 10 minutes, until the fat is rendered. Remove the pan from the oven. If the bacon is not yet crisp return it to the oven for another 2-3 minutes, watching it carefully. Then remove the bacon to a paper-towel-lined plate, reserving the bacon fat.
Place the delicata squash slices onto the sheet pan with the bacon fat in a single layer. Bake for 13 minutes until the squash is beginning to brown. It will brown further in the final baking.
While the bacon and squash are baking combine the cassava flour and soda in a small bowl. In a large bowl combine the mashed butternut squash, water, lemon juice, sea salt, flour mixture, onion, and sage. Mix well.
Reduce the oven temperature to 350 degrees. Add the ground chicken, mixing with a hand mixer until fully combined.
Pour the meat mixture into the prepared pan, smoothing the top. Bake for 25 minutes. Remove from the oven.
Arrange the delicata squash slices on top of the baked meat in the casserole. Crumble the bacon on top. Bake for an additional 8-10 minutes, until the delicata squash is browned. Be careful not to let it burn!
Top the casserole with the fresh thyme. Serve immediately or portion into 8 servings and freeze for later.