1. Preheat your oven to 350°F (175°C) and grease a baking pan.
2. In a bowl, mix the flour, baking powder, and salt.
3. In another bowl, cream together butter and sugar until light and fluffy. Beat in eggs, one at a time, then stir in orange zest, juice, and agave syrup.
4. Gradually fold in the dry ingredients, followed by blueberries and pistachios.
5. Pour the batter into the prepared pan and smooth the top. Bake for 45-50 minutes or until a toothpick comes out clean.
6. Let the cake cool before garnishing with pistachios and orange zest.

Notes: For a gluten-free version, replace all-purpose flour with your preferred gluten-free blend. Adjust sweetness with additional agave syrup if desired.