Preheat the oven to 350ºF.

Make the pesto by placing the spinach, arugula, pistachios, garlic, lemon juice, avocado, and salt into a food processor. Pulse a few times until blended. Turn the machine on and drizzle in the ¼ - ½ cup of olive oil until a creamy consistency is achieved. Taste and add salt as needed.

Place the chicken in a large oven-safe baking dish and cover with the pesto. Bake for 30-40 minutes until cooked through and a meat thermometer registers 165ºF.

Season the cooked spaghetti squash with salt, pepper, and a drizzle of olive oil. Serve topped with the chicken.