Place the sweet potato pieces in a bowl and toss them with olive oil, salt, and pepper. Transfer the potatoes to a 9-inch x 13-inch baking dish and spread them out into an even layer.
Bake for 40 minutes until the potatoes are fork-tender. Stir the potatoes once or twice while they're baking.
When the sweet potatoes have 20 minutes left, place a large skillet over medium-high heat. Cook the diced bacon until it's crispy, about 8 to 10 minutes.
Remove the bacon to a paper towel-lined plate using a slotted spoon. Pour off all but 1 tablespoon of bacon grease, and return the skillet to the heat.
Add the onions and cook until soft and beginning to brown around the edges, about 10 minutes. (If the onions begin to brown too quickly, reduce the heat to medium.) Stir often.
Remove the potatoes from the oven. Add the bacon and onions to the baking dish and then drizzle the syrup over all the sweet potatoes. Gently toss all the ingredients together and season with salt and pepper to taste. Serve warm.