Combine cream cheese, mayonnaise, sour cream, Parmesan cheese, garlic powder, and salt and pepper to taste in a bowl.
Spread the mixture onto a serving plate.
Mix together the minced lettuce with the water chestnuts (if using).
Top the cream cheese mixture with remaining ingredients, in order: lettuce/water chestnut, the cheeses, cooked and crumbled bacon, chopped tomatoes, and green onions.
Chill for at least 2 hours before serving.
Serve with crackers, bread rounds or pita chips.
Note: you can also mix the water chestnuts into the cream cheese mixture instead of into the lettuce, if you prefer.