Preheat the oven to 400 degrees. Cut the garlic in half and drizzle with olive oil. Wrap in aluminum foil. Bake in the oven seam side up for 20-30 minutes until soft and golden brown. Remove it from the oven and allow to cool. Once cool, squeeze out the garlic into a bowl and mash into a paste with a fork, discarding the skins.

In a bowl, make seasoned mayonnaise by combining the roasted garlic paste, mayonnaise, lemon juice, ground fennel, smoked paprika, salt, and Calabrian chilies. Mix well to combine, cover with plastic wrap, and set aside in the refrigerator (this can be made several hours ahead). 

Using a sharp knife, dice the tuna loin into small ¼ inch squares or to the desired texture. Transfer to a large mixing bowl and combine with seasoned mayonnaise. Add more lemon juice and salt to taste if desired. Cover the tuna crudo with plastic wrap and set aside in the refrigerator. 

Slice the bread into 1-inch-thick slices and toast on both sides. Spoon the tuna crudo mixture onto the toasted bread and top with chopped chives, toasted pistachios, and sliced nori paper. Serve immediately. Makes 4-6 servings, depending on the size of the loaf of bread.