Start by preheating your oven to 425F and have a 9"x13" baking tray ready.
Combine in a large bowl, the finely chopped rosemary, the onion soup mix, and the olive oil. Use a rubber spatula to mix the ingredients. Set aside.
Run the potatoes under cold water to remove any excess dirt, and pat them down to dry. Chop them into 1-inch cubed.
Place the cubed potatoes in the large bowl with the onion soup mixture. Use the rubber spatula to fold the potatoes into the seasoning, making sure they are well coated.
Spray a 9"x13" baking tray lightly with non stick spray. Spread the coated cubes of potatoes on the baking tray. Place in the preheated oven for 22 minutes. Toss and flip the roasting potatoes and then bake another 22 minutes.