Pat the cod fillets dry with paper towels and sprinkle both sides with sea salt.
Heat 1 Tbsp avocado oil in a large 12-inch nonstick skillet over medium-high heat.
Place the cod fillets in the hot skillet and cook 3 minutes until slightly golden, then gently flip and cook 3 more minutes; transfer to a plate (they do not need to be fully cooked).
Add a little more avocado oil to the skillet if needed, reduce heat to medium-high, then add the minced garlic and sauté 1–2 minutes until fragrant.
Return the seared cod to the skillet, pour in the 14-oz can of coconut milk, then stir in the lemon zest and 1 Tbsp lemon juice.
Bring the sauce to a boil, then reduce to a gentle boil and simmer 12–15 minutes, stirring occasionally, until the sauce thickens and the cod flakes easily with a fork (cook up to 15–20 minutes for more flavor if desired).
Stir in the fresh basil or spinach and the chopped green onions right before serving, then season with additional sea salt and black pepper to taste.
Serve immediately with your choice of sides.