In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for about 3-4 minutes until translucent.
Stir in the minced garlic, bell pepper, carrots, and celery. Cook for another 5-7 minutes until the vegetables are tender.
Add the diced tomatoes (with their juice), seafood stock, thyme, oregano, and red pepper flakes (if using). Bring the mixture to a boil, then reduce the heat and let it simmer for 15 minutes.
Add the shrimp and fish pieces to the pot. Simmer for an additional 5-7 minutes, or until the seafood is cooked through and opaque.
Stir in the frozen peas and cook for another 2 minutes. Season with salt and pepper to taste.
Serve hot, garnished with fresh parsley.