Preheat the oven to 425F. Lightly oil a rimmed baking sheet or roasting pan.
Slice the sweet potatoes into 3/4 inch rounds. Place on the baking sheet and lightly brush with olive oil. Roast, turning once, for about 15-17 minutes. They should be fork-tender but not mushy.
While the sweet potatoes are roasting, make the glaze. In a small saucepan, whisk together maple syrup, vinegar, pepper and cinnamon over medium heat. Bring to a boil, then remove from heat. Whisk in the butter until melted and the glaze is smooth.
Remove the roasted sweet potatoes from the oven and arange in an ovenproof serving dish. I like to use enamelware, but Pyrex or Corningware also works - as long as it is oven-to-table.
Drizzle the glaze generously over the sweet potatoes.
In a small bowl, mix together the bacon, walnuts and oregano. Sprinkle over the top of the sweet potatoes. Return to the oven for 5 minutes to toast the walnuts and re-crisp the bacon. Serve immediately with any additional maple glaze.