Cook the corn in a large pot of boiling salted water for 5 to 7 minutes, until just tender. Cool for 5 minutes and cut the kernels off the cob, cutting close to the cob with a sharp knife. Place the kernels in a large bowl with the tomatoes, bell pepper, onion, and jalapeno peppers.
In a small bowl or glass measuring cup, whisk together the lime zest, lime juice, olive oil, garlic, chile powder, 1 teaspoon salt, and 1/2 teaspoon black pepper. Pour the dressing over the vegetables and toss.
In a separate bowl, gently toss the avocados and lemon juice together, making sure the avocado is coated in lemon juice. Add to the vegetables, sprinkle with 1 teaspoon salt and 1/2 teaspoon black pepper, and carefully fold together without breaking up the avocados. Sprinkle with salt and serve cold or at room temperature.