Preheat oven to 400 degrees. Line a baking sheet with aluminum foil. Brush cut side of squash with olive oil and season with salt and black pepper. Place cut side down on prepared baking sheet.
Bake until tender and lightly browned, 25-30 minutes.
Meanwhile, bring water, garlic, lemon zest and lemon juice to a boil. Add quinoa, reduce heat to medium-low and cook 12-15 minutes or until almost the water is almost absorbed and the germ is just beginning to appear.
Cover, remove from heat and let stand 10-15 minutes or until cooked and fluffy. Fluff quinoa with a fork and transfer to a bowl.
Add parsley, chives, feta cheese, pistachios and salt and black pepper to taste. Divide filling among squash and serve immediately.
