Seared Tuna Tostadas

Description:

Ingredients:

2 avocados
1 tbsp chopped cilantro plus more for topping
½ tsp salt
¼ head iceberg lettuce, shredded
¾ lb yellowfin tuna (or one large tuna steak)
for the crema:
1 cup sour cream (light)
1 tbsp chipotle in adobo
4 corn tortillas