Place pork and 1/4 cup dressing in a large sealable plastic bag. Remove as much air as possible and seal. Gently knead dressing into meat through the bag. Refrigerate for 1 hour.
Preheat oven to 425 degrees.
Bring a large oven-safe skillet sprayed with nonstick spray to medium-high heat on the stove. Add pork, and discard excess dressing used for marinating. Evenly sear meat, rotating it occasionally, until browned on all sides, about 4 minutes total.
Place skillet in the oven, and bake for 12 minutes.
Carefully flip pork. Bake until pork center reaches 145 degrees, 8-10 minutes.
Meanwhile, clean skillet if needed. Re-spray, and return to medium-high heat on the stove. Add mushrooms and onion, and sprinkle with 1/8 tsp salt and pepper. Cook and stir until partially softened and lightly browned, about 3 minutes.
Add kale and 1/2 cup water to the skillet. Stir. Cover and cook for 3 more minutes, or until kale is tender. Uncover and, if needed, cook and stir until water has evaporated, 2-3 minutes.
Slice pork. Plate veggies, top with pork, and drizzle with remaining 1/4 cup dressing (not the dressing used to marinate the meat) and enjoy!