Preheat an outdoor grill for medium heat and lightly oil the grate.

Roast corn on the preheated grill, turning occasionally, until tender and specks of black appear, about 10 minutes. Remove from the grill and let sit until just cool enough to handle, 5 to 10 minutes.

Holding a corn cob over a large bowl, use a knife to carefully slice warm kernels directly into the bowl; discard cob. Repeat with remaining corn.

Add bell pepper, tomatoes, onion, cilantro, olive oil, salt, and pepper; toss until evenly mixed. Let sit until flavors have blended, at least 30 minutes.