Prepare the lemon Dijon vinaigrette by adding all the ingredients into a small bowl and whisk well to combine. Set vinaigrette aside until ready to serve.
In a large bowl, add the quartered mushrooms, sliced onion, olive oil, salt, pepper, whole garlic cloves and thyme sprigs. Toss to combine.
Select Roast and set the time and temperature to 375°F for 12 Minutes. Press Start.
Once preheated, add the mushrooms and onions into the air fryer basket. Shake the basket a few times during cooking, to ensure even cooking.
When the mushrooms are done cooking carefully remove the thyme stems. You can remove the garlic cloves as well or leave them in the salad.
Place the kale into a large serving bowl and top with the roasted mushrooms and onions. Drizzle the vinaigrette over top and add freshly grated parmesan. Serve immediately.