Place the sugar in a shallow casserole. Place each sardine fillet in the bowl and toss lightly in the sugar. Pat off the excess, discard the sugar and follow the same procedure with the salt. Discard excess salt, place the fillets in 1 layer in the casserole, cover tightly and refrigerate.
Remove from the casserole, and rinse the salt from the fillets. Set on a plate lined with paper towels to remove excess moisture.
In a shallow casserole, combine the citrus juices and zests. Place the fillets in the casserole, making sure that each fillet is completely covered with juice. Cover and refrigerate for 2 days, agitating occasionally to keep fillets moist and add more liquid if necessary, maintaining the 1:2:1 ratio of lime to orange to grapefruit.
Remove the fillets from the citrus bath and discard the liquid. Drizzle the fillets with the 1/4-cup olive oil and set aside.
Bring 1 1/2 cups water to a boil.
Place the bulgar in a medium-sized pot with a lid. Pour the boiling water over the bulgar and immediately cover with the lid. After 5 minutes, remove the lid and fluff the bulgar with a fork, testing it to make sure that it is tender and chewy. Remove to a tray and spread out in a thin layer to cool completely.
When the bulgar has cooled, place it in a large bowl and toss with 2 tablespoons lemon juice, 3/4 cup olive oil and salt and pepper, to taste.
Place the leaves, herbs and fronds in a separate bowl and toss with the remaining olive oil and lemon juice and salt and pepper, to taste.
To assemble the dish, place a mound of the bulgar in the middle of each of 6 chilled dinner plates. Criss-cross 2 sardine fillets over each mound of bulgar, top with a small handful of the salad and serve immediately.
