Place sun dried tomatoes in a bowl and cover with boiling water for 15 minutes until soft, chop.
Whisk together the vinegar, olive oil, and 1 teaspoon of garlic in a small bowl.
In a large serving bowl, add the spinach, sun dried tomatoes, and walnuts.
Heat the vegetable oil over high heat in a large nonstick frying pan and sauté the remaining teaspoon of garlic, mushrooms, and red onions until mushrooms are brown and there is no extra liquid, about 6 minutes.
Add hot vegetables over spinach, add dressing, toss well, and serve immediately.