Peel and dice your peaches. Firmer peaches are easier to peel, and peeling is optional but recommended for texture.
Mix the sugar, corn starch, and cinnamon in another mixing bowl.
Add the peaches and toss to combine. Then, add the lemon and toss to coat.
Pour this mixture over the crust in the baking dish.
Use your hands to squeeze together the remaining dough mixture into larger crumbles and clumps, and sprinkle these over the top of the peach layer.
Bake your bars for 45-50 minutes, until it starts to brown and turn lightly golden.
Remove from the oven and let cool, then put in the fridge to chill until it sets.
Optionally, you can make a quick icing to drizzle over the top.