Remove the husks and silk from the corn. Using a large, sharp knife, carefully cut the ear in half crosswise. One at a time, stand the halves, flat end down, on a cutting board and cut the kernels from the cob.
In a large frying pan over medium heat, warm the olive oil. Add the corn kernels and sauté until the kernels are golden brown, about 10 minutes. Transfer to a bowl and let cool.
Halve, pit and peel the avocados, then cut them into 1/2-inch dice. Add them to the bowl with the corn kernels, add the tomato, green onions and cilantro, and toss to mix. In a small bowl, whisk together 1/2 tsp. of the chipotle, the cumin and vinegar and pour over the corn mixture. Toss gently and season with salt and additional chipotle, if desired.
Serve the salsa immediately, or cover and refrigerate up to several hours. Bring to room temperature before serving. Transfer to a serving bowl and arrange the tortilla chips alongside. Makes about 3 cups; serves 6 to 8.