Melt 1/4 cup of butter in a large skillet over medium-high heat. Add the green onions and saute until soft (2 minutes).
Add the sour cream and Three Cheese Cooking Sauce, stir to combine and cook till it starts to bubble.
Add the sharp cheddar cheese and stir till melted and bubbly again.
Stir in the zucchini and potatoes till they are evenly incorporated. Then pour the mixture into a 9x13" casserole dish.
In a separate, microwavable bowl, melt the remaining 1/4 cup butter in the microwave. Add the panko bread crumbs and toss/stir gently until they are evenly coated with butter. Spread over the casserole potatoes evenly.
Bake for 45-50 minutes. Let cool slightly before serving.