1. Preheat the grill. Break the cauliflower into even-size florets and cook in a saucepan of salted boiling water for 8 minutes, until tender. Drain well and pile into a 1½ litre oven-proof dish with the spring onions and sun-dried tomatoes.
2. Warm the cheese sauce in a saucepan, then pour over the cauliflower.
3. Mix the thyme leaves, breadcrumbs and grated vegetarian parmesan in a bowl. Scatter over the top of the cauliflower cheese, then pop the dish under the grill for 5 minutes, until golden brown.