Start with the filling and placing all the ingredients into a pot over medium heat. Stir occasionally. Cook for 6-8 minutes, the mixture should thicken and the strawberries and rhubarb should be soft. Use an immersion blender or you could use a potato masher to puree the mixture. I like to leave a few small chunks. Transfer to a bowl and chill until ready to use. *You will have extra left over, reserve this for the glaze as well as future use!
Make the dough placing all the ingredients (except the water) into a food processor and pulsing until combined. Add 2 tablespoons of cold water and pulse just until the dough starts to come together. Resist the urge to add more water or this will result in a less flaky dough. Pack the dough together into a disc and then place it between two pieces of parchment paper. Roll the dough out until it's roughly 1/8 " in thickness and use a 2" round cookie cutter to cut out as many circles as you can. Repeat until you have used all the dough.
Place half of the circles onto a baking sheet lined with parchment paper about 1-2 inches apart. Spoon about 1 tablespoon of strawberry-rhubarb filling into the center. Cut 4 small slits into the raiming cutouts and place them over the filling. Use a fork to press the edges together. Whisk together the egg wash and brush it over the pop tarts. Bake at 350 F. for 24-27 minutes and the edges are golden brown. Let cool.
Whisk together the about 1 tablespoon of the remaining strawberry rhubarb filling, almond milk and powdered sugar until smooth and pourable but thick consistency. Add more almond milk if needed.