Make the dressing base: In a jar, combine the very finely minced red onion with the red wine vinegar; let sit 10 minutes to mellow. Zest the lemon first and reserve the zest for garnish (~1 tsp), then juice it (1¼ Tbsp). Add Dijon, lemon juice, and olive oil; close and shake 45 seconds until emulsified. Stir in capers and a pinch of salt and pepper.
Cook the eggs (separate pot recommended): Bring a small pot of water to a boil, lower eggs in gently, and cook 7–8 minutes for jammy yolks. Transfer to an ice bath 5 minutes, peel, and quarter.
Cook the orzo: Boil well-salted water (about 4 qt). Cook orzo 10–12 minutes to al dente. Drain in a fine-mesh sieve and quick-rinse 5–10 seconds to prevent clumping; drain very well.
Steam green beans: Steam 5–6 minutes until tender-crisp; shock in cold water, drain thoroughly, then slice on a bias into 1-inch pieces.
Toast almonds: Toast slivered almonds in a dry skillet over medium-low 2–4 minutes until lightly golden and fragrant; cool.
Prep remaining items: Peel, seed, and slice cucumber into ½-inch crescents. Drain tuna well and flake.
Assemble: Spread orzo on a serving platter and lightly season with salt and pepper. Arrange tuna, eggs, green beans, sun-dried tomatoes, olives, and cucumber over the orzo. Fold in 2 Tbsp chopped dill (reserve the rest).
Dress & garnish: Shake dressing again and drizzle evenly. Toss gently if desired. Garnish with toasted almonds, the remaining ~1 Tbsp dill, and the reserved lemon zest. Serve.