Combine olive oil and lemon juice in a small bowl and whisk to combine. Set aside.
Place corn directly on grill and cook, turning occasionally, until charred on all sides and fully tender (about 10 minutes total). Remove corn from grill and allow to rest until cool enough to handle (about 5 minutes).
Working one ear at a time, hold the corn vertically inside a large bowl and use a sharp knife to remove the kernels. Discard the cob. Add tomatoes, parsley, basil, mint and feta cheese to the bowl. Whisk the dressing and add it to the bowl. Season with salt and pepper and gently fold with clean hands until all the ingredients are incorporated and coated in the dressing. Serve immediately.