1. Prepare the herb marinade by mixing 2 tbsp olive oil, chopped basil, oregano, thyme, lemon zest, lemon juice, salt, and pepper in a small bowl.
2. Pat the halibut fillets dry and coat them evenly with the herb marinade. Let them marinate at room temperature for 20 minutes.
3. While the fish marinates, start the risotto. Heat 1 tbsp olive oil and 1 tbsp butter in a large skillet or saucepan over medium heat.
4. Add the diced onion and sauté until translucent, about 5 minutes. Add minced garlic and cook for another minute, stirring frequently to prevent burning.
5. Add the sliced mushrooms and cook until they release their moisture and begin to brown, approximately 7-8 minutes.
6. Stir in the Arborio rice and cook for 2 minutes to toast the grains lightly, stirring constantly.
7. Pour in the white wine and cook until it is mostly absorbed, stirring constantly.
8. Begin adding the warm broth one ladle at a time, stirring frequently and allowing each addition to be absorbed before adding the next. This process should take about 25-30 minutes.
9. When the risotto is halfway cooked (after about 15 minutes), stir in the chopped spinach, fresh herbs (except for garnish), and continue adding broth.
10. Once the rice is tender but still al dente and the consistency is creamy, remove from heat. Stir in the remaining 2 tbsp butter, grated Parmesan, and heavy cream if using. Adjust seasoning with salt and pepper. Cover and keep warm.
11. Preheat your air fryer to 400°F (200°C) for 5 minutes.
12. Place the marinated halibut fillets in the air fryer basket, ensuring they are not touching. Air fry for 10-12 minutes, flipping halfway through, until the fish flakes easily with a fork and reaches an internal temperature of 145°F (63°C).
13. Remove the halibut carefully to avoid breaking the fillets. Let rest for 2 minutes.
14. To serve, spoon the creamy mushroom and spinach risotto onto plates, place the halibut fillet on top, and garnish with fresh basil leaves and additional lemon zest if desired.