Steam the Mussels: In a large, heavy-bottomed pot, combine 1/4 cup olive oil, the white wine, 1/2 lemon squeezed and dropped in, sliced garlic, and fennel stalks. Add the cleaned mussels, cover tightly and steam over high heat for 3–4 minutes until the shells pop open. Transfer mussels to a bowl (discard any that didn't open), leaving the broth in the pot. Once cool, remove mussels from their shells.

Poach the Shrimp: Bring the seafood broth back to a gentle simmer. Drop the shrimp in and cook 2–3 minutes until pink and opaque. Do not overcook. Remove with a slotted spoon and add to the mussels.

Poach the Scallops: Place scallops in the simmering broth. Cook 2–3 minutes until just opaque throughout. Remove and add to the seafood bowl.

Boil the Potatoes: Add cut potatoes to the same broth (add a splash of water if needed to cover). Boil 10–12 minutes until tender but firm. Remove with a slotted spoon and add to the seafood. Discard fennel and lemon.

Reduce the Dressing: Simmer the remaining broth over medium-high heat until reduced to a concentrated glossy liquid (about 1/4 cup). Pour into a small bowl and whisk in the remaining 2 Tbsp olive oil, lemon juice, mustard, garlic/onion powder, salt, pepper, and red pepper flakes.

Toss and Assemble: Pour the warm reduced dressing over the seafood, potatoes, oregano and parsley. Toss gently so the warm potatoes absorb the flavor. In a separate bowl, lightly toss the greens, fennel and tomatoes with the simple salad dressing.

Serve: Arrange the dressed greens on a platter or in individual bowls. Top with generous spoonfuls of seafood and potato. Serve immediately with crusty bread, or refrigerate 1–2 hours and remove 30 min before serving.