Heat a grill pan over medium-high heat. Brush corn ears with 1/2 tsp. of olive oil each and sprinkle with salt and pepper. Place on the grill and lower heat to medium. Cook, turning regularly, until there are grill marks on all sides (approx. 10 minutes). Remove from heat and set aside for 3-5 minutes (or until cool enough to handle). Using a sharp knife, cut kernels off of the cob.
To assemble salad, combine salad greens, corn, red onion, avocado, cherry tomatoes and chimichurri (to taste) in a large bowl. Toss to combine and serve.