Spray a loaf pan with non-stick cooking spray. In a microwave safe bowl, melt the chocolate for 60 seconds, or until melted. Add the peanut butter to the melted chocolate, and stir together. Next, add the cream cheese, and place the chocolate mixture back in the microwave for 30 seconds. Stir until the mixture is creamy and smooth, (skip this step if using Greek yogurt).
Add the sweetener and cocoa powder, and mix with a spatula until everything is well combined. Spoon the mixture into the prepared loaf pan, and smooth out the top with a spatula. Place the fudge in your freezer for 15-20 minutes, or until chilled.
When fudge is chilled, remove it from your loaf pan and place it on a cutting board or plate. Cut fudge into 12 squares, and cut each of those squares in half, to make 24 squares total.
To make the peanut butter drizzle, place the peanut butter in a small microwave safe dish, and microwave for 30 seconds. Take a fork and drizzle the melted peanut butter over the fudge. Place fudge back in the freezer for about 15 minutes, or until peanut butter drizzle firms up. Keep fudge refrigerated until ready to serve, or wrap up for a gift!