Make the chicken: Place chicken in a large bowl. Add lime juice, jalapeno, garlic, cilantro, and oil, and turn chicken to coat. Cover and refrigerate, turning occasionally, for 1 hour.
Make the corn: Preheat grill to medium-high. Soak corn in cold water for 15 minutes, and drain. Grill corn and scallions, turning both occasionally. Cook scallions until tender, about 5 minutes. Cook corn until husks are brown but not black and kernels are cooked through, about 12 minutes.
Let corn cool slightly, and then husk. Cut kernels from cobs, chop scallions, and combine with oil, salt, and pepper in a medium bowl.
Remove chicken from marinade, and season with the salt and pepper. Grill, turning once, until cooked through, about 3 minutes per side.
Make the lime yogurt: Stir together yogurt and lime juice in a small bowl. Season with pepper.
Assemble wraps: Divide chicken, corn, yogurt, and avocado among lettuce leaves. Serve immediately with lime wedges and cilantro sprigs.
To prevent charring, cut the chicken into small pieces, which will cook quickly.