1 (4 ounce) fillet flounder
salt and ground black pepper to taste
1 pinch garlic powder, or to taste
1/4 cup roughly chopped spinach, or to taste
1/4 tomato, seeded and diced
1 tablespoon chopped onion
1 tablespoon olive oil, or to taste
1 tablespoon balsamic vinegar, or to taste
1 slice mozzarella cheese, cut into cubes
Preheat an outdoor grill for medium-high heat.
Place cod on a piece of aluminum foil and season with salt, black pepper, and garlic powder. Top cod with spinach, tomato, and onion; season again with salt and black pepper. Drizzle olive oil and balsamic vinegar over cod and top with mozzarella cheese. Fold foil over cod creating a packet, crimping the edges together making a seal.
Cook on the preheated grill until fish flakes easily with a fork, 7 to 9 minutes.