Step 1

Preheat the oven to 350℉. Line a 9×9-inch baking pan with parchment paper, leaving about an inch overhang on two sides. Set aside.

Step 2

Make the crumble: In a large mixing bowl, stir together the oats, flour, sugars, baking soda and spices until well-combined.

Step 3

Cut the butter into cubes, then use your fingers to gently knead the butter into the dry ingredients, until completely incorporated, and you’ve formed a shaggy, crumbly dough, that easily sticks together when pinched. This will take a few minutes.

Step 4

Assemble: Scoop about two thirds of the crumble dough into the baking pan, and press into an even layer along the bottom. Spoon the jam over the bottom crust, leaving about 1/4 border around the sides. Top with the chopped strawberries and lemon zest (if using).

Step 5

Sprinkle the remaining crumble mixture over top, from edge to edge. Very gently press the crumbles into the jam.

Step 6

Bake for 35-45 minutes, until the crumble topping is golden brown and has puffed up a bit. The jam may be starting to bubble up through the crumbs, slightly. Remove from the oven and let cool completely before cutting into bars.