Pre-heat oven to 350°F.
In a medium bowl, toss the carrot, parsnip and celeriac in 3 tbsp. olive oil.
Distribute vegetables on a cookie sheet and season with salt and pepper.
Place cookie sheet, covered with parchment paper, in the oven, and roast for about 30 - 40 minutes. tossing occasionally, until the vegetables are fork tender.
In a large Dutch oven, over medium heat, cook the onions and garlic in a little olive oil until softened.
Add the turkey stock, savory and sage to the pot and bring it to a rolling boil.
In a shaker or small bowl. mix the all-purpose flour and water to make a thickening slurry.
Thicken the stock to make gravy by whisking in the thickening slurry; you may not need to use all the flour and water mixture but the gravy should be relatively thick.
Stir in the roasted vegetables, peppers, sweet peas and turkey.
Cook for an additional half hour; serve warm.