Wash, peel, and cut the sweet potatoes into even-sized cubes.
Add the sweet potato cubes to a large mixing bowl and drizzle with 1/2 of the olive oil. Sprinkle with 1 teaspoon cinnamon and toss to coat.
Arrange the sweet potato cubes on a sheet tray and bake for 15-20 minutes. Stir once after 10 minutes.
While the sweet potatoes are roasting, wash and cut the apples into even-sized cubes. Add the cubes to the mixing bowl and drizzle with the remaining olive oil and cinnamon. Toss to coat.
After the sweet potatoes have roasted for 15-20 minutes, add the apples to the pan (or place them on a smaller, separate pan)*, making sure to keep the pieces in a single layer. Return to the oven and bake for another 15-20 minutes, stirring after 10 minutes.
*I've made this recipe several times, but recently cooked the sweet potatoes and apples on separate baking sheets with the sweet potatoes on the bottom rack of the oven. It turned out the best I've ever made it. So you can try separating the two different fruits if you're OK with washing 2 pans!The roasting time may vary with the number of sweet potatoes and apples you use as well as your oven, so be sure to check how soft the pieces are when you stir them and adjust the amount of time in the oven if necessary.If you like your apples crisper, you will want to add them to the pan after 20 minutes. If you want them to be soft like the sweet potatoes, you'll need to add them after 15 minutes.