Rinse the fish fillets, shrimp, and mussels under cold running water. Pat the fish and shrimp dry with paper towels, and set aside. Ensure mussels are clean and remove any that are open and do not close when tapped.
Heat the olive oil in a large pot over medium heat. Add the sliced fennel and chopped onion, sautéing until softened, about 5-7 minutes. Add the garlic and red pepper flakes, cooking for an additional minute until fragrant.
Pour in the white wine, scraping any browned bits off the bottom of the pot with a wooden spoon. Allow the wine to reduce by half, approximately 3-4 minutes.
Stir in the diced tomatoes with their juice and the seafood stock. Bring the mixture to a simmer.
Add the lemon juice and honey to the pot. Season with salt and black pepper to taste. Let the stew simmer gently for about 20 minutes, allowing the flavors to meld.
Add the fish chunks to the stew, simmering for 5 minutes. Next, add the shrimp and mussels, cover the pot, and cook for an additional 5-10 minutes until the shrimp are pink and opaque, and the mussels have opened. Discard any mussels that do not open.
Remove from heat. Stir in the chopped parsley and dill, and garnish with reserved fennel fronds. Taste and adjust seasoning if necessary.