Preheat your oven to 350°F (175°C). Line a muffin tin with parchment liners or lightly grease it to prevent sticking.
In a large mixing bowl, whisk together the flax meal, almond flour, granulated sweetener, baking powder, and cinnamon until well combined.
In another bowl, whisk the eggs, Greek yogurt, and melted butter until smooth. Make sure the butter has cooled down to avoid cooking the eggs.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix.
Gently fold in the raspberries, if using.
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool in the tin for about 5 minutes before transferring them to a cooling rack. Serve warm or at room temperature.
