Marinate the bonito steaks with salt, sugar for about 15 minutes. In the meantime, prep the other ingredients.
In a large shallow pan or dutch oven on medium heat, add oil and saute garlic and shallots until fragrant. Sear the steaks each side for some color. Add the pineapples and tomatoes and young coconut water. You may have to add more or less depending on this size of your pan, just make sure they just barely cover the fish. If you have some prepared nuoc mau, add that now. Bring to gentle simmer and allow liquid to slowly reduce. When it's reduced by about 1/2, adjust final seasoning with fish sauce, thai chile, fresh black pepper. Turn off heat and transfer to serving bowl and top with cilantro and green onion and serve immediately with rice.
Substitute bonito with other meaty fish such as tuna, king mackerel, salmon, swordfish, or monkfish.