In a large salad bowl, toss together the arugula leaves, sundried tomatoes, onions, cheese and avocado.
Whisk together the dressing ingredients until emulsified, then pour into the salad bowl and toss through. Set aside until the mushrooms are cooked.
In a large frying pan, heat a little olive oil over medium-high heat. Stir fry the mushrooms until they start to reduce and release a little bit of their liquid. Then add in the garlic. Add lots of salt and pepper to taste. You can drizzle a little balsamic vinegar (around ½ teaspoon) or squeeze in some lemon juice if you wish. Continue to cook until they are well browned.
Add the mushrooms to the salad, give it a final toss (or you can leave the mushrooms on top, without mixing it together if you prefer) and serve.
