Preheat grill to 350° to 400° (medium-high). Lightly coat corn cobs with cooking spray. Sprinkle with salt and pepper.
Grill corn, covered with grill lid, 15 to 20 minutes or until golden brown, turning every 5 minutes. Remove from grill; cool 15 minutes.
Hold each grilled cob upright on a cutting board; carefully cut downward, cutting kernels from cob. Discard cobs; place kernels in a large bowl. Gently stir in tomatoes and next 5 ingredients. Cover and chill until ready to serve, if desired.
If chilled, let corn mixture stand at room temperature 30 minutes. Peel and chop avocados; toss with corn mixture just before serving. Serve with tortilla chips, if desired.