Line your pan: Line an 8x8-inch baking pan with parchment paper, leaving overhang to lift the bars out later. This keeps the bars from sticking.
Mix dry ingredients: In a large bowl, stir together the protein powder, rolled oats, and a pinch of salt.
Break up any clumps in the powder.
Stir wet ingredients: In a separate bowl, whisk the almond butter, Greek yogurt, honey, and vanilla until smooth and glossy.
Combine: Pour the wet mixture into the dry mixture. Use a sturdy spoon or spatula to mix. If the dough looks too dry or crumbly, add milk 1 tablespoon at a time until it forms a thick, pliable dough.
Fold in the cookie pieces: Gently fold in the crushed sandwich cookies.
If you’re adding chocolate chips, stir them in now or save for a topping.
Press into the pan: Transfer the dough to the lined pan. Use lightly damp hands or a piece of parchment to press the dough evenly into the corners. Aim for an even, compact layer.
Optional chocolate drizzle: Melt the chocolate chips with coconut oil in the microwave in short bursts, stirring between each.
Drizzle over the top and sprinkle with a few extra cookie crumbs.
Chill: Refrigerate for at least 1–2 hours, or freeze for 30–40 minutes, until firm enough to cut.
Slice and serve: Lift the slab out by the parchment and cut into 10–12 bars. Wipe the knife between cuts for clean edges.