Mix together first five ingredients in mixing bowl and set aside.
In a separate bowl whisk greek yogurt, Splenda, oil, egg and vanilla until well blended and Splenda brown sugar is completely dissolved. Slowly add to dry ingredients, mixing in between each addition. Stir in rhubarb.
Spray muffin tins with non-stick spray and fill with the muffin mix. I usually do about 2/3 to full.
In a small bowl combine the last four ingredients and divide the sugar mixture among the muffins.