In a medium sauce pot, combine the black rice and 1¼ cups [2¼ cups] lightly salted water. Bring to a boil, reduce to a simmer, cover, and cook until the rice is tender and the liquid is absorbed, 25 to 30 minutes. Meanwhile, prepare the rest of the meal.

• Trim the root ends from the leek; cut the leek in half lengthwise, then crosswise into ¼-inch-thick half-moons. Soak the half-moons in a medium bowl of cold water, stirring occasionally to loosen any dirt, and allow the dirt to settle at the bottom. Skim the leek from the surface of the water and pat dry.  

In a large frying pan over medium-high heat, warm 1 to 2 tablespoons oil until hot but not smoking. Add the leek, season with salt and pepper, and cook, stirring occasionally, until softened and starting to brown, 4 to 5 minutes. Transfer to a plate. Do not clean the pan. 

While the leek is cooking, prepare the salad.

• Thinly slice the sugar snap peas on the diagonal.
• Zest and juice the lemon, keeping the zest and juice separate. 
• Finely chop the tarragon. Set aside half for the seafood.

In a medium bowl, toss together the snap peas, lemon zest, 1 tablespoon [2 TBL] lemon juice, 1 to 2 teaspoons oil, and half the tarragon. Season to taste with salt, pepper, and more lemon juice, if desired.

• Pat the seafood dry with a paper towel (if using shrimp or scallops, rinse and drain, then pat dry.) Season lightly with salt and pepper (if using scallops, season lightly with salt only).

In the same pan used for the leek, warm 2 to 3 teaspoons oil over medium-high heat (if using scallops, high heat) until hot but not smoking.

Jumbo shrimp: 

Add the shrimp and cook, turning once, until firm and cooked through, 2 to 3 minutes per side.

Scallops:

Add the scallops and cook without turning until golden brown on one side and starting to turn opaque, 2 to 4 minutes. Turn and continue cooking for about 30 seconds for translucent or 1 to 2 minutes for opaque.

Halibut and salmon:

Add the fish (skin side down for the salmon) and cook until lightly browned on the bottom side (and the salmon skin is crisp), 4 to 5 minutes. Turn and cook until the flesh is opaque and flaky, 2 to 4 minutes.

Remove from the heat and sprinkle the seafood with the remaining tarragon and as many Marash chile flakes as you like. 

To the pot with the rice, off the heat, stir in the leek, Parmesan, butter, and 2 tablespoons [¼ cup] warm water. Season to taste with salt, pepper, and any remaining lemon juice.

Transfer the rice to individual plates, top with the seafood, and serve with the tarragon–snap pea salad on the side.