Heat 1 tablespoon olive oil in a saucepan and add the mushrooms. Cook, stirring occasionally, until the mushrooms are wilted. Portion lettuce leaves on salad plates. Top with mushroom slices and Parmesan.
To make vinaigrette, whisk together vinegar, mustard, salt, and pepper. Slowly whisk in 6 tablespoons olive oil. Drizzle on salad immediately before serving.
Source: Come One Come All: Easy Entertaining with Seasonal Menus by Lee Svitak Dean.