Mix together dry ingredients for the cake. (When we're taking this recipe car camping, I put all these ingredients in a plastic zip-top back at home.)
Add water, eggs, oil, and vanilla. Stir until combined.
Pour into a 12" dutch oven. (To save on cleanup, you can line the dutch oven with aluminum foil.)
Dot the top of the cake with the berries. Drizzle lemon juice over berries and sprinkle with lemon zest, if using.
Heat up the water. Stir in the sugar and vanilla. Pour the mixture over the cake and berries. (I'll be honest, while camping I have used cold water in a pinch and just made sure I stirred the mixture vigorously until the sugar dissolves.)
Cover the dutch oven and bake using 8-10 briquettes on bottom and 14-16 briquettes on top for 45 or until the cake has puffed up and the edges are slightly golden. The secret to the gooey pudding layer is not overcooking. Rotate the dutch oven and lid every 10-15 minutes.
Serve warm.