Peel the potatoes, wash, and cut them into even cubes. Transfer them to a mixing bowl and add oil, chopped sage, black peppers, and salt. Mix well.
Spread them now on a nonstick sheet pan evenly and bake at 400F for 15 minutes.
After 15 minutes potatoes are cooked about 90%. Meanwhile prepare green beans.
Clean, & wash them nicely. Trim both the ends & cut into 1.5" lengthwise. Add green beans, oil, chopped sage, black pepper, salt, & sliced garlic to the same bowl and mix nicely.
After 15 minutes, take out the potatoes and add green beans to the sheet pan. Stir everything and spread evenly. Bake for another 15 minutes at 400F temperature.
Once baking is done, take the sheet pan out from the oven and garnish it with cilantro.