Heat vegetable oil in a pot over medium heat. Add onion, garlic, ginger, and scallions. Sauté until fragrant.
Stir in the Korean chili flakes, soy sauce, fish sauce, and sesame oil.
Pour in the broth and bring to a simmer.
Add mussels and cook until they start to open.
Add squid and shrimp, cooking just until opaque.
Gently stir in the tofu and simmer for another 2–3 minutes.
Season with salt and pepper to taste and serve hot.