Tuna Tacos with Avocado and Wasabi Crema

Name: Tuna Tacos with Avocado and Wasabi Crema
Ingredients: 1/2 cup (4 oz./125 g) sour cream; 2 Tbs. heavy cream; 1 1/2 tsp. wasabi paste; 1 Tbs. fresh lemon juice; 1 tsp. low-sodium soy sauce; Kosher salt and freshly ground pepper; 1 cup (3 oz./90 g) shredded green cabbage; 1 cup (3 oz./90 g) shredded red cabbage; 4 tsp. seasoned rice wine vinegar; 1 tsp. mirin; 2 Tbs. olive oil; 1 lb. (500 g) tuna steak, cut into 4 equal rectangular pieces; 8 corn or flour tortillas, warmed; 1 avocado, pitted, peeled and thinly sliced