Preheat oven to 350° Fahrenheit. Lightly grease baking dish with butter or non-stick cooking spray and set aside.
In large skillet over medium-high heat, cook sausage until browned and crumbled. Drain any liquid that's produced.
Add olive oil to skillet with sausage, then stir in onion slices, cooking 2 to 3 minutes until onions are softened.
Add sage, garlic, kale, and chicken stock to skillet. Sauté everything 2 to 3 minutes, stirring occasionally.
While sausage-kale mixture sautés, place butternut squash cubes in baking dish. Pour sausage-kale mixture over butternut squash and toss or stir everything together to combine. Season with salt and pepper to taste.
Add 3 tablespoons butter to skillet over medium-high heat. Once butter is melted and starts to bubble, stir in panko breadcrumbs and continue stirring until breadcrumbs are golden brown and lightly toasted.
Remove skillet from heat and stir in parmesan, sage, salt, and pepper until cheese has melted and ingredients are well combined.
Spread breadcrumb mixture over top of sausage-kale mixture in baking dish. Place in oven and bake approximately 20 minutes. After 20 minutes, cover dish with foil so breadcrumbs don't burn, then return dish to oven and bake 20 more minutes, or until squash is tender. Serve warm.