Brush the ears of corn with the oil. Grill, turning occasionally, until tender and charred in spots, about 15 minutes. When cool enough to handle, use a sharp knife to cut the kernels from the cobs and add them to the bowl with the dressing. (If using frozen corn, simply boil it with the lima beans in the next step.)
To corral stray corn kernels as you cut them from the cob, place the ear of corn inside a deep, large bowl and use a sharp knife to trim downward, collecting the kernels in the bowl.