Remove the frozen spinach from its packaging and thaw it completely. You can thaw it overnight in the refrigerator or use the microwave according to the package directions. Once thawed, place the spinach in a colander and press out as much liquid as possible. For the best texture, squeeze it firmly in a clean kitchen towel. Excess moisture can make the dip watery.
Add the sour cream and mayonnaise to a large mixing bowl. Stir until the mixture is smooth and evenly combined. These ingredients create the creamy base that helps the vegetable seasoning blend distribute throughout the dip.
Sprinkle the Knorr Vegetable Recipe Mix into the bowl and stir well. Add the thoroughly drained spinach, then mix until it is evenly distributed. If using water chestnuts and green onions, fold them in now for extra crunch and a fresh onion flavor.
Cover the bowl or transfer the mixture to an airtight container. Refrigerate for at least 2 hours before serving. Chilling allows the seasoning to hydrate and the flavors to blend. For a stronger flavor, prepare the dip the night before.
Before serving, stir the dip well and taste it. The seasoning mix usually provides enough salt, so additional salt may not be necessary. Transfer the dip to a serving bowl and serve chilled with crackers, sliced vegetables, pita chips, or bread.