Heat olive oil in a large skillet over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic, oregano, and thyme and cook for 1 minute more.
Add spinach and cook until wilted, about 2 minutes. Add half and half and bring to a simmer. Simmer until the liquid is reduced by half, about 3 minutes.
Stir in Parmesan cheese and season with salt and pepper. Remove from heat.
Arrange flounder fillets in a greased baking dish. Top with the spinach mixture and spread evenly over the fish.
Bake in preheated oven until the fish is cooked through, about 10-15 minutes.
Serve hot.
Interesting Facts
Flounder is a type of flatfish that is found in the Atlantic Ocean.
Spinach is a great source of vitamins A, C, and K, as well as iron and calcium.
Parmesan cheese is a type of hard Italian cheese made from cow's milk.