Cut the sweet potatoes, carrots and cauliflower into like sized pieces and place in a large pot and fill with cold salted water. Set on high heat and bring to a boil and cook for about 15 minutes or until the vegetables are very tender. Drain and return pot to heat for a minute or two to evaporate any excess water.
While the vegetables are cooking melt 1 tablespoon of butter with the Splenda and a pinch of salt. Stir in the vanilla and toss mixture with pecans. Arrange on a sheet pan in a single layer and roast for about 5 minutes, watching carefully so they do not burn. Remove and reserve.
When the vegetables are done add half to the bowl of a food processor along with about half of the other ingredients. Pulse until smooth. Transfer to a large bowl and repeat process for the next batch. Blend everything well in the large bowl to make sure the ingredients are distributed evenly. Transfer to a serving bowl and decoratively arrange the pecans on top.