While the fish is cooking, heat a separate cooking pan to medium heat and add butter. Once the butter melts, add flour, minced garlic, and allow to cook for 1 to 2 minutes.
Add white wine (or white cooking wine) and chicken broth and cook for 3 minutes. Add the heavy whipping cream, parmesan cheese, garlic powder, oregano, black pepper, and sea salt.
Zest the skin of the lemon into the sauce and slice the lemon in half and squeeze both halves of juice into the sauce. Cook on low/medium heat until well blended.
Remove the cooked fish and spinach from the foil. Pour on the sauce. Serve hot.