Line a tray: Line a baking sheet or large plate with parchment paper or a silicone mat. Make sure it fits in your freezer.
Mix the yogurt: In a bowl, stir together Greek yogurt, low-carb sweetener, vanilla extract, and a tiny pinch of salt. Taste and adjust sweetness.
If using lemon zest, fold it in now.
Add blueberries: Gently fold in blueberries so they’re coated but not crushed. If adding chopped nuts, fold in a small handful.
Form clusters: Use a spoon or small scoop to drop mounds of the mixture onto the lined tray. Aim for 1–2 tablespoons per cluster.
Optional chocolate drizzle: Melt sugar-free chocolate with a touch of coconut oil in short microwave bursts, stirring until smooth.
Drizzle over the clusters.
Freeze: Place the tray in the freezer for 2–3 hours, or until fully set and firm to the touch.
Transfer to storage: Once frozen, move the clusters to an airtight container or freezer bag. Keep them in the freezer until ready to eat.
Serve: Let a cluster sit at room temperature for 2–3 minutes to soften slightly before biting in for the best texture.