Finely grind the oatmeal in a blender.
Mix lemon juice, Greek yogurt, and oligosaccharide syrup well.
Add egg whites, almond flour, and xylitol sugar to the ground oatmeal and knead the dough.
Spread the dough in a pan and bake in the oven at 180°C for 15 minutes.
Spread lemon yogurt cream on top of the tart.
Refrigerate for at least 1 hour to set.