Heat oven to 350°F. Line an 8-inch square metal baking pan with parchment, leaving a generous overhang.

Pulse the rolled oats 2–3 times in a food processor to make coarse flakes, not flour. Combine with almond flour, oat flour, baking powder and salt.

In a second bowl whisk almond butter, maple syrup, melted coconut oil, vanilla and plant milk. Combine with dry ingredients until a moist crumb forms that holds when pressed. If powdery, add 1 teaspoon milk.

Press about two-thirds of the mixture firmly into the pan in a level layer. Bake 12 minutes until just beginning to set around the edge. Reserve remaining dough for topping.

Meanwhile combine strawberries, maple syrup and lemon juice in a saucepan over medium heat. Cook 6–8 minutes until berries soften and release juices. Mash lightly. Whisk the cornstarch with 1 tablespoon cool water and stir into the berries. Simmer 1 minute until thick. Remove from heat and stir in vanilla and chia; cool 5 minutes.

Spread warm but not steaming filling over the prebaked crust. Crumble remaining dough loosely over the filling; sprinkle with sliced almonds if using. Bake 24–28 minutes until the crumble turns golden and the filling bubbles at the sides.

Cool completely in the pan for at least 60 minutes, then refrigerate 30 minutes before lifting out and cutting into 9 squares with a sharp knife, wiping the blade between cuts.