Slice the mushrooms, the leek and the parsley. Wash the lemon well.
Heat the olive oil in a large skillet over medium-high heat.
Sauté leek and garlic until they start to become tender. Add the mushrooms, lemon zest, lemon juice and sauté for a further for 3 to 4 minutes. Season with salt and pepper to taste.
Then toss in the spinach, stirring constantly for a few minutes, or until spinach is wilted.
Add the vinegar, stirring constantly until it is absorbed, then pour in the white wine. Reduce heat to a low setting and simmer until the wine has been almost completely absorbed.
Sprinkle with fresh parsley.
You can prepare this wonderful dish using only white mushrooms if portobellini are not easily available.