Grilled Shrimp Tacos with Avocado-Corn Salsa

1. 1Remove the corn kernels from the cobs: Place a large container on a damp towel. Fold a paper towel into fourths and place it inside the container. Stand 1 ear of corn on the paper towel, using the stem as a handle. Using a paring knife, slice downward, letting the kernels fall into the container. Rotate the cob and continue until all the kernels have been removed; discard the cob. Repeat with the remaining corn. Discard the paper towel.
2. 2Add the scallions, tomatoes, measured lime juice, cilantro, serrano, and measured salt and stir to combine.
3. 3Halve and pit the avocados. Using a paring knife, score the flesh of the avocado halves in a 1/4-inch-wide crosshatch pattern (be careful not to cut through the skin). Using a spoon, scoop the avocado pieces into the corn mixture and gently fold to combine.
4. 4Taste and add more lime juice or salt as needed; set aside.

For the tacos:

1. 1Heat an outdoor grill to high (about 450°F to 550°F). Meanwhile, assemble the shrimp.
2. 2Whisk the lime juice, oil, chipotle powder, salt, and cumin together in a large bowl. Add the shrimp and toss to combine.
3. 3Skewer each shrimp through the tail and head ends, leaving about 1/4 inch of space between each shrimp. Transfer the skewers to a baking sheet.
4. 4Place the skewers in a single layer on the grill without touching. Close the grill and cook until grill marks appear on the bottom, about 4 minutes. Flip the skewers, close the grill, and cook until the shrimp are just firm, about 1 minute more. Transfer the skewers to a clean baking sheet.
5. 5Remove and discard the skewers, transfer the shrimp to a cutting board, and coarsely chop. Place in a serving bowl.
6. 6Serve the shrimp with the tortillas and salsa.