Preheat the oven to 400°F.
Heat the frozen spinach in the microwave for 5 minutes. Carefully squeeze out as much water as possible and set aside.
Microwave the cream cheese for 1 minute. Combine the cream cheese, mayonnaise, sour cream, cayenne, and garlic powder in a large bowl, and blend together well. Add the spinach, bacon, artichoke hearts, and both cheeses. Stir all the ingredients together until everything is well combined.
Spread the mixture out in a pie or tart plate or in a small casserole dish. Bake for 30 minutes, or until bubbling and slightly browned on top.
Serve hot with crackers, pita crisps, or vegetable sticks, or inside a hollowed-out sourdough bread with the cubed bread on the side.
