Step 1

Preheat the oven to 375°F

Step 2

Spray a 9x13 baking dish with cooking spray or grease with olive oil.In a medium skillet, heat the olive oil over medium heat, until glistening

Step 3

Add the onion and cook stirring occasionally until softened, about 4 minutes.Meanwhile place the shredded zucchini onto the center of a thin kitchen towel

Step 4

Wrap the towel around the shredded zucchini and wring out all of its liquid over the sink

Step 5

You might be surprised how much liquid comes out.In a large bowl mix together the zucchini, cooked onion, salt, nutmeg, dijon, cayenne, pepper, garlic powder, 1/3 cup parmesan, eggs, gruyere cheese and 1/2 cup panko

Step 6

Pour the zucchini mixture into the prepared baking dish.In a small bowl mix together the melted butter with the remaining panko and remaining parmesan

Step 7

Sprinkle it over the top of the casserole and bake in the oven, uncovered for 40 minutes until set in the middle and golden brown on top.