Preheat oven to 350°F and line an 8x8 baking dish with parchment paper in both directions.
Add the oats, almonds, and salt to a food processor and pulse until coarsely chopped. Add the flax & water mixture, honey, and melted coconut oil and pulse to combine. It should hold together and be easy to press into a pan.
Transfer the mixture to the parchment lined baking dish and press into an even layer with your fingers or a spatula.
Bake for 15 minutes, or until the crust is dry to the touch but not browned around the edges yet. Remove from the oven and set aside.
Step 2: Make the Filling
While the crust is baking, add the rhubarb, strawberries, orange juice, and honey to a medium saucepan and simmer for 5-7 minutes, until broken down into a sauce but still a bit chunky.
Mix the arrowroot powder with 2 tbsp of water in a small bowl or cup to help it mix into the sauce better, and add the slurry to the pot. Simmer another minute or so, until thickened.
Step 3: Assemble & Bake
Pour the sauce on top of the baked crust layer. If there is too much, save it and enjoy it on oatmeal or ice cream!
Mix up the oat topping in a separate bowl until well combined, and sprinkle it in an even layer over the fruit mixture.
Bake another 15-20 minutes, or until the top is golden brown and the fruit mixture is bubbly and yummy looking without getting dried out.
Let cool for at least an hour before slicing.
Cut into 6 bars (or 4 for a more filling breakfast) and serve with vanilla yogurt for breakfast, or whipped cream or ice cream if serving these for dessert (or do that for breakfast, I won't tell).
Store these bars in the fridge in an airtight container for a few days, or freeze for up to a month.
To reheat, put them on an oven proof tray in an oven or toaster oven for 10 minutes or so.