4 ears white or yellow corn, shucked
4 medium scallions, thinly sliced (white and light green parts only)
3 medium tomatoes, cored, seeded, and cut into small dice
3 tablespoons freshly squeezed lime juice (from about 2 medium limes), plus more as needed
2 tablespoons finely chopped fresh cilantro
1 serrano chile, stemmed and finely chopped
1 1/2 teaspoons kosher salt, plus more as needed
2 medium avocados
2 tablespoons freshly squeezed lime juice (from about 2 medium limes)
2 tablespoons olive oil
4 teaspoons chipotle powder
1/2 teaspoon kosher salt
1/4 teaspoon ground cumin
2 pounds peeled and deveined large shrimp (about 45 shrimp)
10 (12-inch) skewers (soak wooden skewers in water for 30 minutes to avoid burning on the grill)
16 grilled or warmed corn tortillas