In a large bowl, combine the sliced fennel, fennel fronds, onion, marjoram, and arugula and toss gently to combine. In a small bowl, combine the thyme, oil, orange juice, balsamic vinegar, sea salt, and pepper and whisk well.
Add the cashews to the small bowl and toss to coat. Transfer the salad onto serving plates. Top with orange zest and serve with the thyme vinaigrette on the side.