Combine all citrus cure ingredients in a small, non-reactive bowl. Line a small baking pan with plastic wrap and spoon half the mixture in the bottom. Lay the Kampachi fillet over the cure and cover with the remaining cure mixture. Fold the remaining plastic wrap over the fish and refrigerate for 45 minutes to cure. Remove the Kampachi from the refrigerator and rinse the fillet under cold running water, blot dry with paper towels, brush with olive oil and set aside.
To prepare the vinaigrette, combine all ingredients except the oils and soy sauce in a blender and pulse to combine. With the motor slowly running, add oils to emulsify. Check the seasoning and add soy sauce to taste; reserve. This vinaigrette can be placed in tightly sealed container and stored in the refrigerator for up to one week.
To plate, slice the Kampachi crudo as thinly as possible. Divide between six plates and dress with a few drops of vinaigrette on each. In a small bowl, combine the cucumber, almond slices, corn, blossoms, fennel fronds, and citrus zest and toss gently with three tablespoons of the vinaigrette. Mound the small salads over the Kampachi crudo, garnish with caviar and serve immediately.