Make the rice: in a medium pot, heat the olive oil over medium heat and add the onion and saute for about 3-5 minutes until soft. Add the garlic and saffron and stir until incorporated. Add the rice and chicken stock, bring to a boil and then lower the heat and cover and cook until all the water is absorbed about 30 minutes.
While the rice is cooking make your vinaigrette: Whisk together sherry vinegar, Dijon mustard, and olive oil. Add tarragon, salt and pepper and whisk again. Set aside.
Prepare the ingredients for the salad: In a large bowl combine tomatoes, bell pepper, celery, pimentos, peas, cooked chicken and shrimp.
Add cooked rice to bowl, pour dressing over salad and combine. Adjust seasoning adding salt and pepper to taste. Chill the salad. This salad just gets better with time. Before serving garnish with chopped parsley.