Step 1

Heat 2 teaspoons of the olive oil in a large nonstick skillet set over medium heat. Add the onions and cook, stirring occasionally, until the onions are starting to brown, about 15 minutes.

Step 2

Add the remaining 2 teaspoons of olive oil. Stir in the mushrooms and cook until the mushrooms are tender and the onions are light golden brown, about 10 minutes. Stir in the garlic, rosemary, balsamic vinegar, salt and pepper. Cook for 1 minute.

Step 3

Place the kale in a serving bowl. Add the onion and mushroom mixture, and toss to combine. Serve immediately.