Preheat to 375°F. Prepare pans.
Mix flour, carob, soda, salt, and sugar.
In another bowl, combine oil, water, and vanilla.
Pour the liquid ingredients (but not lemon juice) into dry; mix until blended and smooth.
Add the lemon juice and stir just enough to mix through. There will be pale swirls in the batter. Immediately pour the batter into the pan.
Bake for 25-30 minutes.