1Season fish with salt and pepper. Place in an 8x8x2 or 9x9x2 metal or glass baking dish. Scatter half of the tarragon leaves over the fish. Let sit at room temperature for 10 minutes.
2Bring the broth to a boil in a small pot. Pour over the salmon to submerge. Let stand until cooked to medium-rare, 10-15 minutes. Using a spatula, transfer to a plate and chill.
3Cook sugar snap peas in a pot of boiling salted water until crisp tender, about 2 minutes. Using a slotted spoon, transfer the peas to a bowl of ice water. Let cool; drain. Cut the larger snap peas in half on a diagonal.
4Scoop the avocado flesh in a food processor. Add yogurt, 1 tbsp lime juice, and cumin; puree. Season to taste with salt, pepper, and additional lime juice, if desired.
5Spoon about 1/2 cup avocado puree into the middle of each plate. Mix remaining tarragon leaves, pea, arugula, tomatoes, and shallot in a medium bowl. Drizzle with 1 tbsp olive oil; season with lime juice (if desired), salt, and pepper. Toss; divide among plates. Top with salmon and chives; drizzle each fillet with 1/4 tsp olive oil. Serve with lime wedges.