Preheat the oven to 375 degrees. Coat a 9 x 13 inch baking dish with cooking spray and set aside.

Prepare the enchilada sauce. Heat the oil in a medium pot over high heat. When the oil is shimmering, add the arrowroot powder. Reduce the heat to medium and whisk until combine, about 1 minute. Add the tomato sauce, broth, cumin, chili powder, garlic powder, and salt. Increase the heat to high to bring to a simmer, then reduce the heat to low and cook, stirring occasionally, for 15 to 20 minutes, until thickened.

While enchilada sauce cooks, spiralize the sweet potatoes. Slice halfway through the sweet potatoes lengthwise, careful not to pierce through the center. Spiralize on Blade A to yield chip slices. Set aside.

Spread ½ cup of the enchilada sauce on the bottom of the baking dish. Arrange sweet potato slices in a single layer, overlapping slightly to cover up any little gaps. Sprinkle over with half of the beans, half of the chicken, 1 cup of the cheese, ½ cup of the enchilada sauce, and half of the spinach evenly over the sweet potato slices. Repeat starting with laying out the sweet potato slices and then the beans, chicken, cheese, enchilada sauce, and spinach. Finish the casserole with the remaining sweet potatoes and enchilada sauce. Cover tightly with aluminum foil.

Bake the casserole for 40 minutes, uncover, and sprinkle with remaining 1 cup of cheese. Bake until the cheese melts and casserole bubbles, about 5 minutes. Let cool for at least 10 minutes before serving.

Top with avocado and cilantro. Serve.