Simmer rhubarb, berries, water, sweetener, lemon zest and lemon juice in a medium saucepan over medium heat and cook for about 30 minutes or until the liquid has reduced enough to suit. Stir mixture to breakdown the rhubarb and berries. Taste the mixture and add additional sweetener if desired. It should still retain a little tartness and not be overly sweet because the topping is also sweet.
Serve hot or cold with your favorite cream, yogurt and/or low carb ice cream or serve with muesli and yoghurt for breakfast.
Adjust sweetener to suit your taste. If switching sweeteners and you are using a stevia or monk fruit blend, use the same amount specified in the recipe if they are replacement 1:1 for sugar. If they are a lot more concentrated you may only need to use 2 tablespoons.Recipe can be made using coconut sugar or regular sugar if it fits in with your way of eating.Strawberries or raspberries on their own can be used in lieu of the mixed berries, and can be fresh or frozen. I wouldn't suggest blackberries alone for this recipe.Serves are based on a serving of 2 generous tablespoons. You may find it goes a lot further than 30 serves if you are conservative with your serves.