• Preheat oven to 375℉ and use nonstick spray to grease a 9x13" pan.
• Shred the zucchini and transfer it to a colander. Sprinkle with a light layer of salt, about 1 teaspoon. Top with paper towels and let sit for 15 minutes (or longer) while you measure out remaining ingredients.
  9 Cups Zucchini, 1 teaspoon Salt
• Saute: Heat olive oil in a small skillet over medium heat. Add the onions and soften for 5 minutes. Add the garlic and stir occasionally for 2 minutes. Remove and set aside.
  2 teaspoons Olive Oil, 1 Yellow Onion, 4-5 Cloves Garlic
• Using paper towels, press down and absorb all excess moisture from the zucchini.
• Transfer to a large bowl along with the sauteed onions and garlic, whisked eggs, sour cream, mustard, 1 ¼ cup panko, parmesan cheese, and seasonings/herbs. Stir to combine.
  2 Eggs, ⅓ Cup Sour Cream, 1 teaspoon Dijon Mustard, 1 ¼ Cup Panko Breadcrumbs, ¾ Cup Parmesan Cheese, 1 ½ teaspoons Dried Oregano, ½ teaspoon Dried Thyme, 1 ½ teaspoons Dried Basil, ¼ teaspoon Smoked Paprika, Black Pepper
• Transfer to a lightly greased 9x13-inch casserole dish. Top with cheddar and mozzarella cheese.
  ¾ Cup Cheddar Cheese, ¾ Cup Mozzarella
• Cover and bake for 35 minutes. Remove from the oven and proceed with topping.

Topping

• Combine the 1/3 cup panko and melted butter for the topping and sprinkle it over the casserole.
  ⅓ Cup Panko Breadcrumbs, 1 Tablespoon Butter
• Bake uncovered for 15 minutes.
• If desired, broil at 425℉ for 1-2 minutes to add more color to the top.
• Remove and let stand for 5 minutes then serve.