In a medium bowl, combine the rolled oats (100g / 1 cup), chia seeds (1 tbsp / 15g), and a pinch of salt (1g). Stir well to ensure the chia seeds are evenly distributed and don't clump together.

Add the Greek yogurt (120g / 1/2 cup), milk (240ml / 1 cup), rosewater (1 tsp / 5ml), and your chosen sweetener, honey or maple syrup (1-2 tbsp / 15-30ml), to the bowl with the oats. Whisk everything together until thoroughly combined and smooth. Ensure there are no lumps of yogurt.

Gently fold in most of the chopped pistachios (about 35g / 1/3 cup), reserving the rest (about 15g / 1/4 cup) for topping. This ensures a lovely pistachio texture throughout the oats.

Divide the mixture evenly between two jars or airtight containers (approximately 250ml / 8oz capacity each). Seal the containers tightly.

Refrigerate the jars for at least 4 hours, or preferably overnight. This allows the oats and chia seeds to absorb the liquid, thicken, and soften, creating the perfect overnight oats texture.

Before serving, stir the oats. If they seem too thick, you can add a splash more milk (about 30ml / 2 tbsp) to reach your desired consistency. Taste and adjust sweetness or rosewater if necessary.

Top each serving with the reserved chopped pistachios (15g / 1/4 cup) for a delightful crunch and visual appeal. Serve chilled.