1. Preheat oven to 350°F. Lightly spray a 9x13 inch baking pan and a cookie sheet with non-stick spray.
2. Mix protein powder, flour, oat bran, cinnamon and salt in a bowl. Add in the sweetener. Stir in the chocolate chips.
3. Measure the yogurt, oil and vanilla in a second bowl, stirring until well-combined.
4. Add the wet mixture to the dry and mix patiently until thoroughly blended. You may need to use your hands - it will be a thick batter verging on dough.
5. Transfer mixture to the prepared pan, patting it evenly into place with your hands. Back in the center of the oven for 15 minutes, then remove from the oven and cut into bars of any size or shape. Place the bars on the prepared cookie sheet and bake another 15 minutes or until golden around the edges.
6. Remove the bars from the oven and place them on a rack to cool.
7. Eat the bars within a few hours, or seal them in a heavy zip-style plastic bag and store them in the freezer. They may be re-crisped in the toaster.