Mix the seafood seasoning. Toss the shrimp and scallops in it and set aside.
Heat the oil in a large pot over medium. Add onion, scallion whites, garlic, ginger, and thyme sprigs. Cook 4 to 5 minutes until soft.
Add allspice, cinnamon, and 2 tsp brown sugar. Stir for 30 seconds.
Add the sweet potato, zucchini, squash, bay leaves, broth, the whole pepper, and the crab legs (if using). Bring to a boil, then simmer for 30 minutes, or until the sweet potato falls apart. Pull the crab at 15 minutes and set aside.
Pull the pepper, thyme stems, and bay leaves. Blend in batches with half the coconut milk, blender half full, lid vented with a towel on top. Blend until silky. (Immersion blender works too; see tips.)
Return to the pot over low heat. Stir in the remaining coconut milk. Add soy sauce, lime juice, and coconut brown sugar. Taste, then salt.
Add the shrimp, scallops, mixed seafood (if any), and peas. Simmer 3 minutes until the shrimp are pink and the scallops are opaque.
Serve topped with scallion greens and a squeeze of lime. Add your protein on top (see the meal prep breakdown below).