Pre-heat grill over high heat. Brush both sides of the zucchini slices with half of half of the olive oil (2 tablespoons) and sprinle with salt and pepper. Place seasoned zucchini slices along with the corn on the cob on the grill. Grill zucchini until tender, about 4-7 minutes, turning once halfway through. Rotate corn every 2 minutes until all sides are slightly charred.
Remove the veggies from the grill. Uesing a sharp knife, slice the corn into a large bowl. Next, slice the zucchini into bite-sized pieces and add to the bowl. Add all remaining ingredients to the bowl including feta, basil, scallions, lemon juice and remaining 2 tablespoons olive oil. Toss well and season with salt and pepper to taste before serving.