Thaw the Spinach: Remove the frozen spinach from its packaging and thaw it completely. You can thaw it in the refrigerator or use the microwave according to the package directions.
Remove Excess Moisture: Place the thawed spinach in a clean kitchen towel or cheesecloth and squeeze firmly to remove as much liquid as possible. This helps keep the dip thick and creamy rather than watery.
Soften the Cream Cheese: Place the softened cream cheese in a large mixing bowl. Beat with a hand mixer or whisk until smooth and free of lumps.
Add the Creamy Ingredients: Add the sour cream and mayonnaise to the cream cheese. Mix until everything is evenly combined and the mixture has a smooth consistency.
Season the Dip: Stir in the garlic powder, onion powder, salt, black pepper, and lemon juice. Taste the mixture and adjust the seasoning if needed.
Fold in the Vegetables: Add the well-drained spinach, chopped water chestnuts, and green onions. Fold gently with a spatula until the vegetables are evenly distributed.
Chill Before Serving: Cover the bowl and refrigerate the dip for at least 30 minutes. Chilling allows the flavors to develop and gives the dip a firmer consistency.
Garnish and Serve: Transfer the chilled spinach dip to a serving bowl. Garnish with chopped green onions and serve with crackers, bread slices, or fresh vegetables.