Turn oven on to start heating to 230 C / 450 F / Gas Mark 8.
Scrub potatoes and sweet potatoes, but don't peel them. Cut into medium-sized chunks and toss into roasting pan.
Scrub the parsnips, but don't peel them. Quarter them and toss into roasting pan.
Peel the onions, but don't cut the root end off. Quarter them and toss into roasting roasting.
Peel the garlic cloves and toss into roasting pan.
Add the oregano, thyme, rosemary, and 2 tablespoon of the oil. Toss everything together then place in oven to roast.
Making the dressing by combining the remaining 4 tablespoon of olive oil, vinegar, capers and mustard. Set it aside.
Now pour yourself a cuppa and pull out a good book.
After the vegetables have been in the oven for 1 ½ hours, quarter the tomatoes and toss them in on top the other vegetables. Let everything roast for a final ½ hour.
When done, divide the roasted veg amongst 4 plates, divide and scatter the salad green over top of each, and drizzle each plate with the dressing. Serve hot or warm.
Notes
Instead of rocket (arugula), you can use watercress, or omit the leafy green bit altogether.