Step 1

Pulse chiles in a food processor until finely chopped (if you’d rather chop them by hand, wear gloves!). Transfer to a small bowl.

Step 2

Grind mushrooms in a spice mill or with a mortar and pestle (or use food processor again) to a powder.

Step 3

Hold coconut in one hand and strike it firmly around the equator with the back (blunt side) of a heavy knife or cleaver, rotating coconut as you go until it splits. Whack coconut halves with the back of knife to loosen meat from shell. Remove meat and shred on the large holes of a box grater (or use food processor fitted with grating plate). Toast shredded coconut in a dry wok or large cast-iron skillet over medium heat, stirring often, until deeply browned in spots, 15–20 minutes. Transfer to another small bowl.

Step 4

Heat oil in same wok over medium-low. Cook scallions, garlic, and ginger, stirring constantly, until very fragrant, about 3 minutes. Mix in chiles, mushroom powder, toasted coconut, lime leaves (if using), sugar, and salt. Cook, stirring often, until golden brown and very fragrant, about 5 minutes. Let cool.

Step 5

Do Ahead: Palapa can be made 3 months ahead. Cover and chill.

Step 6

Toss shrimp with 2 cups palapa in a large bowl. Cover and chill at least 1 hour or up to 1 day.

Step 7

Prepare a grill for medium heat; oil grate. Arrange shrimp on grate and pack any palapa still in the bowl on top; season lightly with salt. Grill, turning once or twice and keeping as much palapa on shrimp as possible, until opaque all the way through, about 5 minutes.

Step 8

Meanwhile, grill lemon halves, cut side down, until charred, about 5 minutes.

Step 9

Serve shrimp with lemons for squeezing over.