Preheat oven to 350°F Generously spray a 9- by 13-inch baking pan with cooking spray.
Place Bisquick in a medium-sized mixing bowl. Stir in the eggs and oil. Mix until the batter is smooth.
Add the spinach, onion, garlic, oregano, cheese, and salt and pepper. Stir lightly to blend.
Pour the batter into a baking pan and bake until golden brown and firm, about 30 minutes.
Pie may be served warm or at room temperature. Cut the pie into squares when you are ready to serve and arrange them on a platter decorated to look like the bottom of the sea. Sprinkle bread crumbs on the bottom of the platter, place seaweed squares on top, and arrange some seashells around the perimeter.