Preheat a grill to high. Toss 1 pound baby bell peppers or quartered regular peppers with 2 tablespoons olive oil; season with salt and red pepper flakes. Grill, turning, until blistered, about 10 minutes. Transfer to a bowl and toss with 1 tablespoon olive oil, some chopped mint and the juice of 1/2 lemon. Top with crumbled feta.