Heat the oven to 350 °F. Line a baking sheet with parchment paper.

Make the filling: Combine the strawberries, maple syrup and lemon juice in a saucepan. Cook over medium heat until thickened, up to 30 minutes. Mash the fruit if desired. Let cool completely, then stir in the chia seeds, if using.

Pulse the oats in a food processor until finely chopped. Add the flour, flaxseed, baking powder and salt and pulse to combine.

In a measuring cup, whisk together the melted coconut oil, maple syrup and egg. With the processor running, pour the liquid through the feed tube and process until a sticky dough forms, adding non-dairy milk a splash at a time if it won't come together. Scrape down the sides and pulse again to combine.

Turn the dough onto plastic wrap or parchment paper, press into a flat disk and wrap well. Refrigerate for at least 30 minutes or up to several days.

Cut the chilled dough in half, keeping one half wrapped. Roll the other half between two sheets of parchment into a 6-by-12-inch rectangle, trimming and rerolling as needed. Spoon the fruit filling down the center third, then fold each side over the filling like a letter, pressing any cracks closed. Cut into 4 bars and transfer to the baking sheet. Repeat with the remaining dough and filling.

Bake until golden brown and baked through, 15 to 20 minutes. Let cool completely on the baking sheet. Store in an airtight container at room temperature for up to 1 week.