Lobster Toasts With Avocado and Espelette Pepper

Name: Lobster Toasts With Avocado and Espelette Pepper
Ingredients: Kosher salt; One (1 1/2-pound) live lobster or 8 ounces pre-cooked lobster meat; 3 tablespoons mayonnaise; 1 tablespoon crème fraîche; 2 teaspoons lemon juice, divided; 1/2 teaspoon finely grated lemon zest; 1 teaspoon finely chopped tarragon, plus more (for sprinkling); 1 teaspoon finely sliced chives; 1 Hass avocado; Six (1/2-inch thick) slices brioche (4 ounces), crusts removed; Piment d'Espelette or cayenne pepper (for sprinkling)