In a small bowl, whisk together vinegar, mustard, garlic, salt and pepper. Gradually whisk in oil until mixture thickens. Set aside.
In a medium-size bowl, mix together beans, tomatoes, parsley and 2 tablespoons of the dressing.
Place salad blend, onion and mushrooms in a large bowl and toss with the remaining dressing. Divide among 4 plates and top with bean mixture. Microwave bacon 1 minute; crumble 2 slices over each plate.