1/4 cup red wine vinegar
1/4 cup balsamic vinegar
1/4 cup tomato juice
1 Tbsp. olive oil
2 tsp. Dijon mustard
2 tsp. stone-ground mustard
1/4 tsp. coarsely ground pepper
4 large portobello mushroom caps (about 5 inches wide)
1 Tbsp. Cajun seasoning for steak (such as ChefPaul Prudhomme's Steak Magic)
2 tsp. olive oil
16 cups gourmet salad greens
1 large tomato -- cut into 8 wedges
1/2 cup thinly sliced red onion -- separated into rings
1 (15-ounce) can cannellini or other white beans -- rinsed and drained
1/4 cup (1 ounce) crumbled blue cheese
Combine first 7 ingredients in a large zip-top plastic bag. Add mushrooms to bag; seal. Marinate 10 minutes, turning occasionally. Remove mushrooms from bag, reserving marinade.
Sprinkle mushrooms with Cajun seasoning. Heat 2 teaspoons oil in a large nonstick skillet coated with cooking spray over medium-high heat until hot. Add mushrooms; cook 2 minutes on each side or until very brown. Cool; cut mushrooms diagonally into thin slices.
Arrange 4 cups salad greens on each of 4 plates. Top each with mushroom slices, 2 tomato wedges, and onion rings. Sprinkle each with 1/4 cup beans and 1 tablespoon blue cheese. Drizzle the reserved marinade evenly over salads.