Preheat the oven to 175C and line a baking tray with parchment paper. In a bowl mix together the olive oil, lemon juice, ground cumin, paprika, garlic powder, mixed herbs, chilli flakes, salt and pepper. In a separate bowl, combine the mushrooms and walnuts. Pour the marinade over the mushroom and walnut mix, toss to combine. Spread the mix onto the parchment paper and bake for 20-25 minutes until crispy. At the 10 minute mark, mix the crumbles so they cook evenly on all sides. Remove from oven and set aside.