Using a cheese grater, roughly grate the vegan butter into thick slivers. I do this on a cutting board so that I can spread out the slivers. Refrigerator for later use.
Combine the flour and salt into a food processor. Pulse to combine. Add the chilled butter and pulse until the butter is combined. The mixture should be crumbly with obvious small flakes of butter.
Add the ice water 1 tbsp at a time. Pulse until a dough forms. I usually find that I need ~4 tbsp of ice water.
Form the dough into a ball and wrap it in plastic. I like to use a clean, recycled bread bag. Allow the dough to chill in the refrigerator for at least 1 hour.
While the dough is chilling, add 2/3rds of the strawberry slices and all of the rhubarb to a medium-sized sauce pan. Add the sugar and lemon juice and stir until the fruit is thoroughly coated. Bring the fruit to a low simmer, stirring occasionally. As the fruit releases its moisture, it will become syrupy. After 10 minutes, remove the fruit from the heat and stir in the chia seeds. Rest in the refrigerator until ready for use.
Preheat your oven to 400º.
Prepare a baking sheet with parchment paper or a silicon baking sheet. After an hour, remove the dough from the refrigerator and allow it to warm up slightly. When it is pliable, roll the dough out into an oval/circle shape that will fit on your baking sheet. Don’t worry about it being perfect! That’s the beauty of a galette. Transfer the pie crust to the baking sheet.
Spread the strawberry rhubarb jam on the pie crust leaving only 1-1 ½” inches of the edges free from the jam. Lay the sliced strawberries on top of the jam and then fold the edges of the crust over the outer edge of the jam. Roughly pleat the crust as you go.
Melt 1 tbsp of vegan butter in the microwave. Using a basting brush, generously spread the vegan butter on the outside edges of the galette. This will give the crust a nice browned appearance. Then sprinkle 1 tbsp of sugar over the crust and top of the galette.
Bake the galette on the middle rack for about 30 minutes. It is done when the crust is golden brown. Remove the galette from the oven and transfer the baking mat or parchment paper to a cooling rack. Allow the galette to cool for at least 30 minutes. Then slice and enjoy!