Preheat oven and a large roasting pan to 220°C fan forced. Add the mushrooms to the hot pan. Add the thyme and drizzle over 2 tbs of the olive oil, shake the pan to coat all the mushrooms. Roast 15 minutes or until the mushrooms are just tender.
Meanwhile, heat a medium non-stick frying pan over medium heat. Add 1 tablespoon oil and the cashews, cook, shaking the pan for 3-4 minutes until cashews light golden. Add the honey and sesame seeds and toss gently to coat. Remove cashews to a tray lined with baking paper to cool.
Add the cashews, tomatoes and spinach to the mushrooms. Combine the remaining 2 tablespoon olive oil, vinegar, mustard and salt and pepper in a screw-top jar, shake to combine. Pour the dressing over the mushroom salad and toss gently to combine. Serve warm or at room temperature with roast turkey, pork or ham.