Combine the water, chopped rhubarb, maple syrup, vanilla and salt in a medium saucepan over medium heat. Bring to a simmer and cook covered for about 10 minutes. Once soft, remove from heat, stir in the coconut oil, coconut sugar, lemon zest, lemon juice, and stir to achieve a uniform liquid. Lastly, add the chia seeds, stir well to combine, and set aside.
Preheat oven to 350°F / 175°C.
In a large bowl combine oats, buckwheat, and coconut flakes. Roughly chop almonds and add them to the mix. Pour liquid ingredients over dry and fold coat.
Spread mixture out in an even layer on a lined baking sheet and press firmly with the back of a spatula to ensure that the mixture is compact. Bake for 15-20 minutes. Remove from oven, flip granola in large chunks, and place back in oven to bake for another 10 minutes, stirring every 3-4 minutes until toasted and fragrant, about 45-50 minutes total. Turn off the oven and allow to cool completely -- this will result in a super-crunchy batch. Make sure to check on it though as it still can burn at the beginning of the cool-down process.
Once cool, add the freeze dried strawberries, if using. Give it all a good toss to combine, then store in an airtight glass container for up to one month.