Line a large baking tray (with sides) with foil, and spray with cooking spray.
Put the sausage slices, onions, and potatoes into a large bowl. Drizzle with a couple TBS of olive oil and season to taste with salt, pepper, paprika and dried thyme. Toss together & pour on to the baking tray.
Place into the preheated oven and roast for 45 minutes to an hour, stirring half way through, until the potatoes are golden brown and tender.
Scatter the cheese over top, & put back into the oven a few minutes to melt the cheese.