Heat your oven to 200°C/Fan 180°C/Gas 6. Trim and peel the parsnips, then chop into pieces about the size of a little finger. Scatter the parsnip into a roasting tin and toss with 1 tbsp oil and a good pinch of salt and pepper. Slide into the oven and roast for 10 mins.
Meanwhile, trim any woody bases and dry outer leaves away from the sprouts. Slice them in half.
Peel and finely slice the red onion and slide into a bowl. Drain the butter beans and rinse well with cold water. Shake dry and add to the onions. Grate in the lemon zest and squeeze in the juice. Peel and grate in the garlic clove. Pour in 1 tbsp oil and sprinkle in a pinch of salt and pepper. Give everything a good stir and set aside.
When the parsnips have roasted for 10 mins, remove the roasting tin from the oven and turn them over. Scatter in the sprout halves and return to the oven for a further 10 mins.
Scatter the flaked almonds into the roasting tin with the parsnips and sprouts and return to the oven for a final 5 mins, till the nuts are toasted.
Add the roast veg to the bowl with the beans and onion and toss together. Fold in the rocket leaves. Pile the salad onto plates and serve.