Heat oil in a large pot over medium heat and sauté minced ginger and green onion until fragrant, about 1 minute.
Add mixed seafood to the pot and cook for 2 minutes until the surface firms up.
Pour in chicken broth and add cubed tofu, bring to a boil, then reduce heat to medium-low.
Add green peas and simmer for 5 minutes until tender.
Add mushrooms and simmer for 2-3 minutes until mushrooms are tender.
Season the soup with salt and black pepper to taste.
Mix cornstarch with 2 tablespoons of water to create a slurry, stir into the broth, and cook until thickened, about 1 minute.