Preheat oven to 375 degrees. Line a rimmed baking sheet with parchment paper.
In a small bowl, whisk together 1 Tbsp. sesame oil and 2 tsp cornstarch. Cut wonton wrappers in half and place on rimmed baking sheet. Brush on oil mixture and then sprinkle wonton wrappers with sesame seeds. Bake in oven for 5 minutes or until golden brown. Remove from oven and let cool.
Meanwhile, in a small bowl, combine 1/2 cup soy sauce with ginger. Place tuna steaks in soy sauce mixture and marinate for 10 minutes. Remove tuna from marinade and discard marinade. Season tuna steaks with salt and pepper.
Heat remaining 1 Tbsp. oil over medium heat in skillet. Add tuna steaks and sear on all sides. Remove from pan and transfer to cutting board. Thinly slice tuna and brush with remaining soy sauce.
Place tuna slices on wonton crisps. Top with wasabi sauce and sliced serrano peppers.