1 tablespoon red wine vinegar (or freshly squeezed lemon juice)
1/4 cup shaved parmesan
In a pan over medium high heat, add 1 tablespoon olive oil. When the oil is hot, add mushrooms and cook for 5 minutes, or until mushrooms are golden brown. Turn the heat off and let cool the mushrooms cool to room temperature.
Whisk the remaining two tablespoons olive oil with the vinegar until the mixture has emulsified. Set aside.
In a large bowl, add spinach and dressing and toss until the leaves are evenly coated. Add shallots and mushrooms and toss well.
Season with salt and pepper and top with shaved parmesan.