Dressing: Whisk the vinegar, mustard, sugar, salt, garlic, dried tarragon, black pepper and chilli flakes in a small mixing bowl until smooth. Pour the safflower oil into the dressing in a thin steady stream while whisking vigorously until the oil has been fully incorporated into the dressing; set aside.
Rice: Bring the wild rice and water to a boil in a saucepan over high heat. Reduce heat to medium-low, cover and simmer until the rice is tender but not mushy; 20 to 45 minutes depending on the variety of wild rice. Drain off any excess liquid, fluff the rice with a fork and cook uncovered 5 minutes more. Scrape into a mixing bowl and refrigerate until cold.
Chicken and Peas: Stir the chicken, celery, parsley and spring onion into the cooled wild rice. Stir in the dressing until evenly blended. Cover the rice mixture and refrigerate 4 hours to overnight.
Bring a small saucepan of lightly salted water to a boil. Add the sugar snap peas and cook uncovered until just tender; about 30 seconds. Drain in a colander then immediately immerse in ice water for several minutes until cold to stop the cooking process.
Once the peas are cold, drain and cut into 2cm diagonal pieces. Refrigerate until ready to serve.
Stir the peas and toasted almonds into the rice mixture just before serving.