preheat your oven to 200 celcius or about 390 farenheit.
Coat your potatoes with the olive oil and sprinkle with salt and pepper. You can also add additional spices to taste, I used smoked paprika and garlic powder, but this is completely optional. Also if you want you can add sprinkle the potatoes with some rosemary.
Now place the potatoes on a baking dish and put them in the oven for about 20 minutes depending on the size of your oven and potatoes. When you can easily poke them with a fork and the skin is a bit crisp, but not burnt, they are done.
While the potatoes are in the oven you can make the lentils and avocado.