Cut off leaf end of each strawberry, making sure to create a flat surface. Make an x-cut in the pointed end of each strawberry, making sure not to cut all the way through.
Combine softened cream cheese and goat cheese, mayonnaise, brown sugar, black pepper and spinach. Stir until smooth. Stir in walnuts. Pipe or spoon a small amount cheese mixture into the pointed end of each strawberry.
Garnish with additional chopped walnuts, if desired. Refrigerate. Bring to room temperature before serving.