In a medium bowl, combine the cilantro, jalapeno, ginger, garlic, lime juice, soy sauce, sugar, salt, pepper, and 2 tablespoons of olive oil. Stir the ingredients together until well incorporated.
In a skillet over medium-high heat, coat pan with the remaining 2 tablespoons of olive oil. Season the tuna generously with salt and pepper. When hot, sear tuna for about 1 minute then flip.
While searing on the other side, pour 1/2 of the cilantro mixture into the pan to coat the fish. After 1 minute, remove and serve with the sliced avocado and the remaining cilantro sauce drizzled over the whole plate.