Preheat the oven to 375°F (190°C). Lightly coat a baking dish with cooking spray or a drizzle of olive oil.
Bring a large pot of water to a boil. Carefully add the sweet potato slices and parboil for about 8 minutes, until just tender but still firm enough to hold their shape. Drain well.
While the sweet potatoes cook, heat a little olive oil in a skillet over medium heat. Add the beef sausage, breaking it apart with a spoon. Cook for about 8 minutes, or until browned and cooked through. Remove from the heat.
Slice the apples into thin wedges. Toss them with 1 teaspoon of cinnamon, a pinch of salt, and black pepper. Add a small splash of olive oil and toss to coat.
For the sweet potato sausage casserole, arrange half of the parboiled sweet potatoes in the bottom of the prepared baking dish. Add half of the cooked sausage, apples, and chopped pecans.
Repeat with the remaining sweet potatoes, sausage, apples, and pecans.
Sprinkle the shredded cheddar evenly over the top. Scatter any remaining pecans over the cheese.
Cover the dish loosely with foil and bake for 30–35 minutes. Remove the foil during the final 5 minutes so the cheese and pecans can become lightly golden.
Remove from the oven and let the casserole rest for 5 minutes before serving.