To more easily peel and cube the butternut squash, pierce it with the tip of a knife. Place on microwavable plate. Microwave uncovered on High 1 to 2 minutes; let stand 2 to 3 minutes. Carefully use a heavy, sharp knife to cut off the stem. Peel the squash with a vegetable peeler, then use the knife to cut it in half. Use a teaspoon to scoop out seeds and membrane, then cut into cubes.
Once you’ve used your slow cooker a few times, you will begin to better anticipate how small to cut the vegetables. For example, in this recipe, if you prefer the squash very tender, cut the cubes a little smaller.