Place a large roasting pan in the oven then preheat oven and pan to 220°C fan forced. Add the mushrooms to the hot pan. Add thyme and drizzle over 2 tbsp of the olive oil, shake the pan to coat all the mushrooms. Roast mushrooms for 15 minutes or until tender.
Meanwhile, heat a medium non-stick frying pan over medium-heat. Add 1 tbsp oil and the cashews, cook, shaking the pan for 3-4 minutes until cashews are light golden. Add the honey and sesame seeds, 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 tbsp 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.