Place corn into a large pot of cold water. Cover and bring to boil. Reduce heat and simmer for 20 minutes. Drain corn.
To char corn, place directly over the flame of a gas grill or onto a hot BBQ. Turn as it chars. You just want to get a little color on the corn and not completely burn it. Remove from heat and cut kernels off the cob and into a large bowl. Stir in red pepper, radishes, cilantro, and scallions.
For the dressing, whisk all ingredients together and toss with corn mixture. Serve immediately or cover and refrigerate until ready to eat.