Preheat the oven to 350°F (180°C). Lightly grease a 9×13-inch (23×33 cm) pan and line it with parchment paper, leaving some overhang on the sides to make it easier to lift the bars out once set.
In a large bowl, combine the flour, oats, baking powder, and salt.
Add the butter, honey, and vanilla.
Use a fork or pastry cutter to combine the ingredients.
Mix until the mixture is crumbly and evenly combined.
Add about ⅔ of the crumb mixture into the prepared pan.
Press firmly into the bottom of the prepared pan to form the crust.
Place the cranberries in a bowl.
Add the honey, orange juice and orange zest and toss to coat.
Add the cornstarch and toss again until evenly coated.
Spread the cranberry mixture evenly over the crust.
Sprinkle the remaining ⅓ crumb mixture over the cranberries.
Bake for 40–50 minutes, or until the top is lightly golden and the filling is bubbling at the edges. If the top browns too quickly, loosely cover with aluminum foil during the last part of baking.
Let the bars cool completely in the pan before cutting into squares.
Store leftovers in an airtight container at room temperature for up to 2 days, or refrigerate for up to 4 days.