Begin by taking a large mixing bowl and adding the Greek yogurt, peanut butter, honey (or maple syrup), and vanilla extract. Using a whisk or a spatula, mix these ingredients together until the mixture is smooth and thoroughly combined.
In a separate bowl, combine the rolled oats, protein powder, and a pinch of salt. Whisk these dry ingredients together until evenly mixed.
Gradually introduce the dry mixture into the yogurt mixture, stirring continuously until just incorporated. If you opted for nuts and chocolate chips, gently fold them into the combined mixture to ensure even distribution.
Prepare an 8x8 inch (or similar size) baking dish by lining it with parchment paper. This ensures easy removal of the bars once they have set.
Pour the blended mixture into the lined baking dish. Using a spatula, spread the mixture evenly, pressing down firmly to compact it nicely.
Cover the dish with plastic wrap or aluminum foil to prevent drying out and place it in the refrigerator. Allow it to chill for at least 2 hours, enabling the bars to firm up.
Once the mixture has set, remove it from the dish using the edges of the parchment paper. With a sharp knife, cut into squares or rectangles of your desired size for serving.
Notes
Serve on a platter and drizzle with honey or melted dark chocolate for added flair.