Position a rack in the middle of the oven and pre-heat the oven to 375ºF.
Drizzle the grape tomatoes with 1 tablespoon EVOO and season with salt, pepper and thyme. Roast in the oven for around 20-25 minutes.
Meanwhile, heat the remaining EVOO over medium-high heat. Brown the bacon, then remove to a paper towel-lined plate. Reserve some of the bacon drippings and melt in 2 tablespoons butter. When the butter foams, add the leeks and wilt for 5 minutes; season with salt and pepper.
Gently fold the roasted tomatoes, bacon and leeks into mashed potatoes and parsnips. Season with salt and pepper, to taste.