For the radish and peas: Melt the butter in a saute pan and gently cook the radishes until half cooked. Add the peas with 1/4 cup/60 ml water. Continue cooking until the peas and radishes are tender. Season, and scatter over the green onions and dill.
For the fish bundles: Lay the lettuce leaves in a saute pan of boiling salted water for a few seconds. Remove, and immediately plunge in an ice bath. Lay flat on tea towels to drain, gently patting them dry. Remove the ribs, so you have strips of lettuce. Lay a few leaves on a board, slightly overlapping. Lay a fish fillet on top. Season, and neatly fold the lettuce leaves over to make a neat package, with the end of the fish visible out the ends. Make the other 3 bundles. If you're not cooking until much later, wrap and refrigerate. Otherwise, just set them aside.
To cook the fish: Lay the fish bundles in a bamboo steamer over a saucepan of 2-inches/5 cm boiling water. Steam until the fish is just cooked, about 10 minutes. Serve with the sauce alongside the fish passed in a sauceboat. A bed of radishes and peas is the perfect accompaniment.
For the sauce: Put the dill stalks, shallot, garlic, wine, and stock in a saucepan. Boil to reduce by 3/4. Strain, and return the liquid to a clean saucepan. Add the cream and simmer to sauce consistency, about 5 minutes. Remove from the heat. Whisk in the butter a piece at a time. Taste, and season with salt, pepper, and lemon juice, if needed.
For the plate: Enjoy a piece of fish and a tumble of radishes and peas side by side on a plate.