1. Heat olive oil in large skillet. Add Brussels sprouts and season with salt. Sauté Brussels sprouts until brown on all sides, about 4 minutes.
2. Add vinegar and maple syrup to the skillet and heat thoroughly. Add spinach and toss with Brussels sprouts mixture until it softens, about one minute. Remove skillet from heat and transfer to serving platter. Season with salt if necessary and sprinkle with pistachios.