Preheat oven to 375 degrees F (190 degrees C).

Trim off ends of squash; cut squash in half (lengthwise). With a teaspoon scoop out seeds and part of the pulp leaving shells about 1/2 inch thick. Steam squash shells over boiling water until crisp-tender (about 5 minutes). Plunge into cold water, drain well and set aside.

In a small frying pan over medium heat, melt one tablespoon of the butter. Add onion and garlic and cook until they are done. Squeeze the spinach to remove extra moisture and add to the garlic and onion and cook until thoroughly heated.

In a medium size mixing bowl, combine eggs, ricotta, Parmesan, parsley, salt, pepper, Italian seasoning and spinach mixture. Fill the squash halves with this mixture, about three tablespoons per shell and place squash in a shallow baking dish. Melt the remaining butter and brush over the squash shells

Bake for 20 minutes. If desired, serve with tomato sauce.