Zucchini Imperial

This recipe goes way back in our family, originally introduced by my mother back in the 70s.  As a hearty side dish it pairs well with my favorites, steak or salmon, but it would also be good or ham and chicken.  The picture shows it without the breadcrumbs or panko topping as an option - I do highly recommend the addition for a nice crunch.  Enjoy!

6 Cups, sliced, steamed, well-drained zucchini (4-5 good sized zucchini) or squash or a combination  of both. I usually stick with the zucchini only.
1 cup mayo (I use the one made with olive oil)
1 cup shredded Parmesan Cheese
2 beaten eggs
1/2 teaspoon salt
1/4 teaspoon pepper
1/2 cup chopped onion (or 1/4 cup minced dried onion)

Optional topping:
1/2 cup bread crumbs or Panko
2 Tablespoons melted butter

Combine all ingredients except for zucchini in a large bowl and mix well. Add zucchini and fold gently until it is well-combined.  Be careful to be gentle as the vegetables can turn mushy easily. Pour into a greased 2 qt. casserole.  Sprinkle with topping.  Bake in a 375 degree oven for 35-40 minutes or until center is set. The edges will brown considerably so watch it closely at the end so it doesn't over-bake.  Serves 4-6.