Heat olive oil in a large stock pot over medium heat. Add shallots and sauté for 2–3 minutes or until translucent. Stir in garlic and cook for 30 seconds.
Deglaze pan with white wine then add tomatoes, broth, thyme, chili flakes, sea salt, and pepper. Bring mixture to a gentle simmer and cook for 5 minutes. Adjust seasoning to taste at this point.
Add mussels and shrimp and bring stew back to a gentle simmer. Cook for 1 minute then add cod. Continue to cook until shrimp is opaque, mussels are open (discard unopened ones), and the cod flakes.
Serve promptly with crusty bread and lemon wedges, if using.