Rinse quinoa under cold water until water runs clear. Combine quinoa with 2 cups water in a small saucepan. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes or until water is absorbed and quinoa is tender. Remove from heat and let sit covered for 5 minutes. Fluff with a fork.

While quinoa cooks, gently rinse and drain spinach. Steam spinach over boiling water for 2-3 minutes until wilted and tender. Set aside and keep warm.

Pat cod fillets dry with paper towels. In a small bowl, mix olive oil, lemon juice, oregano, salt, and pepper. Brush or spoon half of the mixture onto both sides of the cod.

Heat a nonstick skillet over medium heat. Cook cod fillets 3-4 minutes per side or until opaque and flakes easily with a fork. Avoid overcooking to keep fish tender.

Serve cod fillets over a bed of quinoa with steamed spinach on the side. Drizzle remaining lemon herb mixture over the spinach if desired.