Veggie Squares

My best friend Jim loves these and can eat a whole batch in one sitting.They are a great cold appetizer but also make a nice light lunch or supper.
Note:The spinach and mushrooms are optional, my version of this recipe.I think they really add something and are a big hit with my friends.

1 1/4 cups Bisquick
2 cups fresh spinach , chopped
Or 1 pkg frozen, thawed and squeezed dry
4 large eggs slightly beaten
1 cup sliced mushrooms.
2 cups thinly sliced zucchini
1/2 cup finely chopped onion
2 cloves finely minced garlic 
1/2 cup vegetable_oil
1/2 cup grated parmesan_cheese
2 tsp minced parsley                                                        
11/8 tsp black_pepper
3/4 tsp salt
1/2 tsp ground oregano