Heat large skillet over medium-high heat, then add 2 tablespoons of avocado oil or other neutral cooking oil. Add mushrooms and cook until golden brown around the edges. Remove mushrooms to large bowl.
Add remaining salad ingredients—arugula, lentils, red onions— to mushrooms bowl and toss to combine.
Make Mustard Miso Dressing
Whisk together the Miso Mustard Dressing ingredients in a small bowl, food processor or blender. Add water 1 tablespoon at a time until the dressing is a pourable consistency.
Drizzle about half of the dressing over the salad, and toss everything together. Add more dressing a few tablespoons at a time if needed to coat all the vegetables.
Nutrition information per serving includes salad with dressing.Cabbage Apple Salad without dressing has 68 calories, 2 g protein, 0 fat, and 5 g fiber per serving.