Make the marinade: in a container large enough to hold the chicken breasts, combine the olive oil, lime juice, onion, garlic, oregano, and salt and pepper. Pour half of the marinade into a cup or small container and refrigerate, covered, while you finish the salad. Add the chicken and the jalapeno peppers, turn to coast the chicken and peppers well, and refrigerate, covered, for about 3 hours.
Preheat the grill to medium high. Remove the chicken and the peppers from the marinade. Add the corn to the grill along with the chicken and peppers, and grill for about 6 to 12 minutes in total (the peppers will take about 6, the corn 8 to 10 minutes the chicken 10 to 12 minutes), turning the corn, chicken and peppers frequently as they develop grill marks. Remove from the grill when until the chicken is cooked through, the corn has nice brown char marks in spots, and the peppers are softened and have char marks all over the outside. Remove the chicken, corn and peppers to a plate and allow to cool to just warm or room temperature.
Peel the jalapeno peppers (if using), discard the core, seeds, and inner ribs and mince the peppers, then add them to the reserved dressing. Stir or shake to combine. Slice the kernels from the corn cobs.
Assemble the salad: Slice the chicken breasts crosswise. In a large bowl toss the lettuce with half of the reserved dressing, then place it on a large shallow serving bowl or platter. Peel and thinly slice the avocados. Arrange the chicken, avocados, tomatoes, corn, onions and feta attractively over the salad. Or, you can divide the ingredients between 6 plates, if you’re going restaurant-style. Drizzle over as much of the rest of the dressing as you like.
Notes
The jalapenos are optional, but if you have the grill going they will cook at the same time as the corn and chicken. They will blister up and char as you turn them. Then, once they are cool, they can be peeled seeded and diced and minced, then added to the reserved dressing. They add wonderful smoky heat, but with the seeds and removed they won’t blow the roof off spicy-wise. If you love hot pepper heat, leave a bit of the seeds in!