Using the back of a knife, lightly smash lemongrass and ginger. Cut lemongrass into 4-inch pieces.
Bring lemongrass, ginger, lime leaves or lime peel and broth to a boil in a large saucepan. Reduce heat and simmer until flavors are melded, 8–10 minutes.
Strain broth into clean saucepan or use a slotted spoon to remove solid ingredients. Discard solids.
Mix in coconut milk, fish sauce and sugar. Whisk to incorporate coconut milk.
Reduce heat, add mushrooms and peppers and simmer until mushrooms are slightly soft, 10 minutes.
Add shrimp and simmer until they are cooked, 6-8 minutes. If using small bay scallops, add them with the shrimp. If using large sea scallops, sear them in ghee while the shrimp is cooking.
Divide soup among bowls over rice. Top with seared scallops.
Serve with chili oil, cilantro and lime wedges.
