Season tuna steak with salt and pepper to taste, and sear all sides of the tuna in a hot pan with 1 tablespoon olive oil for about 1 minute. Remove from heat.
To prepare Caper Dressing, place first 6 ingredients in a blender on low speed to combine. Slowly add olive oil with blender running until it is completely emulsified with the other ingredients.
Place arugula on serving plate, put seared tuna on top and arrange vegetables and hard boiled egg around it. Pour dressing over all and garnish with fresh dill. Serve immediately.
