Yellowtail Crudo with Citrus and Avocado

• 1 avocado
• 1 garlic clove, chopped
• 1 tablespoon crème fraîche or sour cream
• 2 serrano chiles, seeded, finely chopped, divided
• 2 tablespoons fresh lime juice, divided
• Kosher salt
• 4 ounces sashimi-grade skinless, boneless yellowtail fillet
• 2 teaspoons olive oil
• 1 teaspoon fish sauce
• 1 teaspoon finely chopped shallot
• ½ teaspoon finely grated peeled ginger
• ½ teaspoon yuzu kosho
• 1 radish, trimmed, thinly sliced
• Cilantro leaves with tender stems and thin fancy crackers or crispbread (for serving)

Ingredient Info

• Yuzu kosho can be found at Japanese markets and some specialty foods stores.