Preheat the oven to 180°C / 350°F.
Place the potatoes in a large baking pan, about 12 inches / 30 cm in diameter or another pan of similar capacity. Season with salt and pepper.
Arrange the chicken pieces on top of the potatoes.
In a jar or bowl, combine the olive oil, lemon juice, garlic, mustard, oregano, and salt. Shake or whisk well.
Pour the sauce evenly over the chicken and potatoes.
Add the water to the jar, swirl to collect any remaining sauce, and pour it into the side of the pan.
Sprinkle the chicken with black pepper.
Cover the pan tightly with a lid or parchment paper and foil.
Bake for 1 hour 20 minutes.
Remove the cover and continue baking for 40–45 minutes, until the chicken is golden, crispy, and beautifully roasted.
During the final bake, baste the chicken with the pan juices 3–4 times for extra flavor and moisture.
