In a small saucepan with 1 3/4 cups water, add 1 1/2 cups corn kernels and a large pinch of salt. Bring to a boil; lower heat and cook until very soft, about 20 minutes. Place corn and cooking liquid in a blender; puree until very smooth, adding several tablespoons water if too thick. Strain through a coarse-mesh sieve into a small bowl. Stir in wasabi paste. Add salt to taste. Makes about 1 cup.

Place remaining 1/2 cup corn kernels in a saucepan with enough water to cover. Cook over medium heat for 10 minutes.

Meanwhile, rub salt into both sides of tuna steaks. Coat a large nonstick skillet with cooking spray. Heat skillet over medium-high heat until hot. Add tuna and sear each side, about 3 minutes. Remove tuna from heat and place on a platter.

Reheat sauce, adding salt to taste. Drain corn. Pour sauce over fish and scatter cooked corn on top. Serve immediately.