Sprinkle tuna fillets with salt and pepper on both sides and set aside.
In a mixing bowl, mash avocado with a fork and mix in diced tomatillos. Stir in shallot, lime juice, salt, and pepper. Set aside until fish is finished.
In another mixing bowl, combine cilantro, ginger, shallot, lime juice, tamari sauce, salt, pepper, and coconut oil.
Heat a large skillet over moderately high heat. Add 1 to 2 tablespoons of oil or ghee to heated skillet.
Place fillets in heated skillet for 1 minute on each side. Turn fillets sideways to ensure that all sides have been seared.
Pour cilantro marinade mix into the skillet and coat the fish on both sides. Do not overcook.
Remove the fillets from the skillet. Either cut fillets in half or into thin slices and fan out on plates. Drizzle remaining marinade from the skillet onto the fish.
Top with guacamole and serve.