Preheat your oven to 350°F (175°C). Grease the 9x13 inch baking pan or line it with parchment paper for easier removal.
In a large mixing bowl, combine the cake mix, vegetable oil, water, and eggs. Mix with an electric mixer on medium speed for about 2 minutes, until smooth and well-blended.
Pour half of the cake batter into the prepared pan, spreading it evenly.
In a medium bowl, mix the softened cream cheese, powdered sugar, and vanilla extract until smooth. Add the milk gradually and stir until you have a creamy mixture.
Spoon the cream cheese mixture over the cake batter, creating a layer across the pan. Make sure it is evenly distributed but do not mix into the batter.
Spoon the remaining cake batter over the cream cheese layer, then swirl the batter gently with a knife to create a marbled effect.
Scatter the sliced strawberries, coconut, and nuts (if using) on top of the cake batter.
Bake in the preheated oven for 40-45 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 15 minutes before serving. Cut into squares and enjoy!