To make the chili water, place all ingredients into a small pot and bring to a boil. Remove from heat and allow to cool. Once cool, store in a sealed bottle in the refrigerator for up to one month.
To make the corn pudding, place kernels in a food processor or blender and puree until smooth. Pass corn through a fine strainer, pressing the solids against the strainer or chinoise with the back of a ladle to extract all of the juice. Discard any solids. In a small pot, heat corn juice over medium heat until thickened. (The naturally occurring starch will thicken the pudding.) Let pudding cool. Season to taste with lime juice and sea salt. Can be stored in refrigerator for up two days.
Whisk to combine all ingredients for the marinade. Add ahi and marinate in the refrigerator for 30 minutes to 1 hour before serving.
To plate, place a large spoonful of corn puree onto each serving plate. Top with a serving of ahi, and garnish with corn kernels, avocado, a few slices of onion and macadamia nuts.