Preheat your oven to 350°F (175°C). Line a standard muffin tin with silicone liners or spray it generously with non-stick cooking spray. This is essential since there is no crust to hold the cups together.
In a medium mixing bowl, whisk together the eggs, Greek yogurt, sugar-free maple syrup, and vanilla extract until the mixture is smooth and well-combined.
Add the protein powder, ground cinnamon, and salt to the wet mixture. Stir gently until the powder is fully incorporated and there are no large clumps remaining. Be careful not to overmix if using whey protein, as it can become rubbery.
Gently fold in most of the chopped pecans, leaving a small handful aside to sprinkle on top. Ensure the nuts are evenly distributed throughout the batter.
Divide the batter evenly among 6 muffin cups. Sprinkle the remaining pecan pieces on top of each cup. Place in the oven and bake for 18-22 minutes, or until the centers are set and the edges are slightly golden.
Remove the tin from the oven and allow the cups to cool completely in the pan. They will firm up as they cool, making them much easier to remove without breaking.