In a spice grinder or clean coffee grinder, coarsely grind each type of peppercorn separately. Transfer to a small bowl, and toss to combine. Set aside.
In another small bowl, mix vinegar and mustard; add 6 tablespoons oil in a slow steady stream, whisking continuously. Season to taste with salt and pepper, and set dressing aside.
Fill a large bowl with ice and water. Bring a large pot of salted water to a boil. Add haricots verts, and cook until bright green and just tender, about 1 minute. Using a slotted spoon, lift beans from water, and transfer to the ice bath to cool. Remove from ice bath with slotted spoon; transfer to a clean kitchen towel. Pat dry; transfer beans to a large bowl. Set aside.
Return the water to a boil. Add fava beans, and cook until just tender, 2 to 3 minutes. Drain and transfer to the ice bath. Drain in a colander. Remove and discard inner skins from fava beans, and add beans to haricots verts.
Sprinkle scallops with salt and reserved peppercorn mixture. Heat a cast-iron skillet until very hot over medium-high heat. Add 1 1/2 teaspoons olive oil. Add half the scallops, and cook until well browned, 2 to 3 minutes on each side. Transfer to a plate, and set aside.
Add remaining 1 1/2 teaspoons olive oil to the skillet. Repeat with the remaining scallops, and transfer to the plate.
Add olives, onion, tomatoes, and reserved dressing to beans; toss to combine.
Arrange salad on six plates. Top with eggs and scallops; garnish with tarragon. Serve with lemon wedges if desired.