Line a large baking sheet (I use a 15 x 10 x 1 inch jelly roll pan) with aluminum foil and spray with non-stick cooking spray. Place diced potatoes on the foil-lined pan.
Drizzle the olive oil over the potatoes, and then using your hands (or a spatula) toss the potatoes until they are completely coated.
Sprinkle the pepper, salt, and rosemary over the potatoes, and once again use your hands to toss the potatoes until they are evenly distributed.
Place pan in the oven and cook for 35-45 minutes, stirring every 10-15 minutes so that they are evenly cooked and don't get burned on one side.
When finished baking, remove from oven and sprinkle with additional salt and pepper if desired.