Arrange zucchini slices in overlapping concentric circles on four dinner-sized plates. Drizzle zucchini lightly with extra virgin olive oil (about 1½ teaspoons per plate), then season each plate with a pinch of salt and freshly ground black pepper. Divide crumbled feta and walnuts over each dish, and then sprinkle with fresh dill. Serve immediately with lemon wedges.