Preheat your oven to 350°F. Lightly grease the bottom of a 9 × 13-inch baking dish.
Arrange the sliced sweet onions in a single layer across the bottom of the prepared baking dish.
Place the chicken thighs skin-side up over the layer of onions.
Evenly pour the bottled Russian dressing over the chicken thighs, using a spoon to make sure each piece is well coated with the sauce.
Cover the baking dish tightly with aluminum foil and bake in the preheated oven for approximately 45 minutes.Carefully remove the foil.
Spoon some of the sauce from the bottom of the dish over the chicken thighs.
Return the uncovered dish to the oven and bake for an additional 25–35 minutes, or until the chicken is fully cooked and reaches an internal temperature of at least 165°F.
