Step 1Combine the vinegar, sugar, shallot, garlic, pepper and salt in a mixing bowl. Slowly drizzle in the oil until incorporated. Refrigerate until using. (Makes 1 cup.)
Step 1Heat the oven to 350 degrees.
Step 2Arrange the bread slices on a baking sheet. Sprinkle with the Parmesan, oregano and pepper. Drizzle with the oil.
Step 3Toast in the oven until the cheese is melting and the bread is slightly charred, 10 minutes.
Step 1Wipe the portabello, cremini and shiitake mushrooms clean. Cut the portabello mushroom caps into 1- to 1 1/2-inch pieces. Combine all the mushrooms in a bowl with 1/2 cup of the dressing, tossing to coat. Let marinate 1 hour.
Step 2Heat a grill pan over medium-high heat. Grill the mushrooms until softened, 3 to 5 minutes, turning often. You can use a grilling basket or rack to make this easier.
Step 3Place the greens, 2/3 of the Gorgonzola and the walnuts in a mixing bowl. Toss with the remaining 1/4 cup of dressing.
Step 4Divide the croutons among 4 servings plates and top with the greens. Remove the mushrooms from the grill, place on top off the greens, and sprinkle with the remaining gorgonzola.