Simmer rhubarb, berries, lemon zest, lemon juice and sweetener in a saucepan over medium heat and cook for 8-10 minutes until the rhubarb starts to breakdown. Stir mixture to combine and set aside to cool slightly. 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.
To make the crumble, melt the butter until it goes a light golden color. Add the sweetener and simmer gently for about 2 minutes. Remove from heat and allow to cool for a few minutes. Add the almond meal, coconut, slivered/flaked almonds and salt to the butter mixture. Using a fork, roughly combine to form a chunky crumble mix. Use fingers to squeeze mix if desired to create larger chunks of crumble.
Place the rhubarb berry mixture into a baking dish and top with the crumble mixture. Bake for 20 minutes or until golden and fruit mixture is hot. If topping isn't crisp enough up the temperature towards the end for a few minutes. Note that this will cook a lot quicker than a regular crumble mix so keep an eye on it for excess browning.
Serve hot with your favorite cream and/or ice cream.
Notes
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 can be used in lieu of the mixed berries, and can be fresh or frozen.Do not over cook your butter and sweetener as some sweeteners will crystallize if cooked for too long.If your crumb mixture is too wet, add some additional almond flour to get a drier consistency. Different almond meals/flours can have different absorbency levels.If you have a brown sugar sweetener substitute, you could use the rub in method to make your crumble instead of melting the butter. If you aren't concerned about caramel flavors you could also use this method for the recipe using the sweeteners that are specified as well.For a general family meal I like to make this as one dish. Visually, these look fabulous when served in individual pots.