Preheat oven to 400 degrees Fahrenheit. Bring a large pot of salted water to a boil. Add pasta and cook until al dente.
In a medium saucepan over medium-high heat, melt 1 tablespoon of butter. Add the milk, nutritional yeast, lemon juice, mustard, onion powder, garlic powder, salt and pepper. Whisk briskly. Slowly whisk in the arrowroot starch. Simmer until sauce begins to thicken - about 5 minutes.
Add the mozzarella shreds and slowly whisk until melted. Add the squash and whisk until everything is combined and heated through. Add the cooked pasta to the sauce - stir gently - salt further to taste.
Pour mixture into an ovenproof baking dish - 9”x9” square dish or similar.
In a saucepan melt remaining butter. Add bread crumbs and toss to coat well, then sprinkle evenly over the pasta. Top with a sprinkle of paprika.
Bake for 15 minutes or until the sauce begins to bubble.