Preheat a fryer to 360 degrees F. Begin by mixing the cumin and pepper in a small bowl. Dip and coat each tuna steak in the cumin mixture. In a hot skillet coated with oil, sear each tuna steak for approximately 2 minutes on each side. Remove from the pan and set aside. The tuna should still be pink.
In a hot wok or skillet, saute the diced pineapple and red bell pepper for 2 minutes. Remove from wok and set aside.
Prepare the tempura batter right before you are ready to fry. The avocados should be peeled and sliced into 1/2-inch thick slices. To make the batter, mix the flour, egg, and cold water together until all of the ingredients have combined. Dip each avocado piece into the batter and fry until golden, approximately 1 minute. Remove the fried avocado pieces and season.
To make the wasabi sauce, combine the wasabi paste and heavy cream in a small saucepot. Bring the sauce to a boil and let reduce. Once the sauce has reduced you are ready to serve.
To serve this dish, place the avocado tempura in the center of each plate. Top with tuna and surround with the seaweed. Add a spoonful of the pineapple and peppers, and drizzle some of the wasabi sauce around the plate.