Preheat the oven to 180°C.
Peel the parsnips and cut them into long wedges. Spread them out on a baking tray in a single layer.
Cut the mushrooms in half and add them to the parsnips.
In a small bowl, mix together the mustard, olive oil, lemon juice, honey (or date syrup) and minced garlic.
Pour the dressing over the vegetables and toss well to coat everything evenly. You can use a silicone brush to distribute the dressing.
Season with salt and pepper.
Bake for about 20 minutes, or until the parsnips are tender and lightly golden.
Serve warm with chopped parsley scattered over the top.