Preheat your oven to 350°F (180°C) and line a large baking sheet with parchment paper.
In a single large bowl, add the egg, granulated sweetener, and vanilla extract. Whisk vigorously for 30 seconds until slightly pale and combined.
Add the crunchy peanut butter, ground flaxseed, cinnamon, and sea salt to the bowl. Use a spatula to fold and mix everything together until a cohesive, stiff dough forms.
Gently fold in the sugar-free chocolate chips.
Scoop small portions of dough (about 1 tablespoon each) and roll them into 24 uniform balls. Place them on the prepared baking sheet, leaving space between them.
Using the back of a fork dipped in water (to prevent sticking), gently press down on each ball to flatten it, then press again in the opposite direction to create a classic criss-cross pattern.
Bake for 9-11 minutes. The cookies will be very soft and appear slightly underdone in the center, but the edges will be set and golden.
Allow the cookies to cool on the baking sheet for at least 10 minutes to firm up completely before transferring them to a wire rack.