Whisk the lemon rind, juice, oil and caster sugar together in a large bowl. Season. Add the mushrooms and stir to coat. Cover and refrigerate 1 hour or until mushrooms have absorbed dressing.
Meanwhile, squeeze the tomato seeds and juice over the burghul. Stir to combine. Cover and stand for 15 minutes. Finely dice the tomato flesh and chop the parsley and mint.
Add the tomato, herbs, green onions and burghul to the mushrooms. Season, toss gently to combine. Serve with barbecue steak, chicken or seafood.