Preheat oven to 350°F (175°C) and lightly coat a standard 9x5 inch loaf pan with non-stick spray.
In a large mixing bowl, combine the self-rising flour, 40g of the vanilla protein powder, and the Greek yogurt using a spatula until a cohesive dough forms.
Turn the dough onto a lightly floured surface and roll it out into an approximately 12x8 inch rectangle.
In a small bowl, whisk together the cinnamon, sweetener, and the remaining 20g of protein powder to create the filling mixture.
Sprinkle the filling mixture evenly over the dough, leaving a 1/2-inch border at the edges.
Roll the dough tightly starting from the shorter side and place it seam-side down into the prepared loaf pan.
Bake for 25 to 28 minutes until the loaf is golden brown and firm to the touch.
Remove from the oven and let cool in the pan for 10 minutes before slicing into 8 equal portions.