Combine ingredients: In a small mixing bowl, whisk together the egg, peanut butter, and vanilla extract until smooth and well blended, about 30 seconds.
Add cheese and sweetener: Fold in the shredded mozzarella cheese and monk fruit sweetener, stirring gently until the mixture is evenly combined with no lumps of cheese remaining.
Let it rest: Allow the batter to sit for 1 minute so the cheese can slightly soften and integrate, making the batter easier to cook evenly.
Preheat the iron: Heat your waffle iron to medium-high heat for about 2 minutes until it's hot and ready to use.
Prepare the iron: Lightly grease the waffle iron with cooking spray or a tiny amount of butter to prevent sticking.
Pour the batter: Divide the batter evenly between the waffle iron molds, using about half the mixture per chaffle for two chaffles total.
Cook until golden: Close the lid and cook for 4-5 minutes, watching for steam to slow down, which signals the chaffle is nearly done and edges are turning golden brown.
Remove carefully: Using a silicone spatula or plastic utensil, gently lift the chaffle from the iron and place on a cooling rack or plate.