Low calorie yes. Low sugar? Maybe. High protein? That's up to you.
This is how I make these, I haven't tried subbing in protein powder for some of the oats or cocoa powder because I don't think they would taste right and there is always the potential problem of damaging the protein powder by heating it too much.
180g (3/4 cup) Low fat yogurt
60ml (1/4 cup) Skimmed milk (or almond/soy)
64g (1/2 cup) Unsweetened Cocoa powder
43g (1/2 cup) oats
64g (1/2 cup) brown sugar (or sweetener of your choice)
1 free range egg
1 tsp Baking powder
Pinch of salt optional
Optional 150g Roughly chopped pecans (or nuts of your choice)
Blend together (except the nuts) and place in a greased a 6x6 baking tray. Cook at 200c/400f for 15-20 mins depending how gooey or cake like you prefer.
I cut into 9 pieces.
With my choice of ingredients I get a relatively thick brownie 2"x2" that has approx 80 calories and 3G fat (without nuts but made with sugar)