In a medium bowl, whisk together vinegar, parsley, mustard, salt, pepper and red pepper flakes. While whisking, add oil in a thin stream. Set aside.
Bring a saucepan of water to a boil. Add beans; cook for 3 to 4 minutes. Drain and rinse with cool water.
Place shrimp in a resealable plastic bag or glass dish. Add 1/4 cup of the dressing and toss to combine. Marinate at least 10 minutes while heating grill or broiler. Thread shrimp onto skewers or place on broiler pan. Grill or broil for 5 minutes, turning, until cooked through.
In a medium bowl, toss green beans, tomatoes and feta cheese with 1 tbsp of the remaining dressing. Place arugula and red onion on a serving platter or in a large bowl. Top with shrimp and season with salt. Drizzle with 2 tbsp of the dressing and add green bean mixture. Serve remaining dressing on the side, if desired.
Opt for bottled light red wine vinaigrette or light Greek dressing and add a pinch of cayenne.