Pre-heat oven to 400°F and line a large, rimmed baking sheet with parchment paper or a Silpat® baking mat. Set aside.
In a large mixing bowl, combine potatoes, red onions, minced garlic, olive oil, and fresh rosemary. Generously season with salt and black pepper, to taste, and arrange the veggies on the prepared baking sheet in a single layer.
Add the chicken thighs to the large bowl and coat with any remaining rosemary and olive oil mixture. Season the chicken with additional salt and black pepper, if desired, and nestle in between the veggies along with the lemon wedges and sprigs of fresh thyme.
Roast in the pre-heated oven for 30-35 minutes, or until the veggies develop nice color and the chicken is nearly done. Remove baking sheet from the oven and stir in the fresh kale.
Return the sheet pan to the oven and roast for another 10-12 minutes, or until the chicken is completely cooked and the kale is wilted.
Remove from oven and transfer chicken and potatoes to a serving platter and loosely cover with foil. Let chicken rest for 5 minutes before serving. Enjoy!