In a large pot, bring water to a boil. Add a pinch of salt.
Add the shrimp to the boiling water and cook for about 2-3 minutes until they turn pink and opaque. Be careful not to overcook.
Drain the shrimp in a colander and run under cold water to stop the cooking process. Set aside to cool.
In a medium mixing bowl, whisk together the olive oil, lemon juice, Dijon mustard, salt, and pepper to create a dressing.
In a large salad serving bowl, combine the mixed greens, cherry tomatoes, cucumber, red onion, parsley, and cooled shrimp.
Drizzle the dressing over the salad and toss gently to combine all the ingredients evenly.
Top with sliced avocado just before serving.