Place quartered zucchini wedges in a large mixing bowl, then drizzle with avocado oil, Kosher salt, and freshly ground black pepper. Place shucked corn and seasoned zucchini wedges directly on grill grates, then cook.
Allow the corn and zucchini to cool for about 5 minutes, then use a sharp knife to cut the kernels off of each ear of corn. Slice the zucchini. Place in a large mixing bowl.
To the zucchini and corn, add crumbled feta, chopped toasted walnuts, and thinly sliced scallions. Drizzle with basil vinaigrette, then toss to thoroughly coat.
Taste and adjust seasoning as needed. Serve immediately or at room temperature with a generous pinch of flaky sea salt.
Feel free to top with additional feta, walnuts, or scallions!