In a medium saucepot, cover potatoes with water and heat to boiling; cook 20 minutes. Drain and spread potatoes on sheet pan to cool.
Preheat oven to 400 degrees F. Butter a 9-inch deep-dish pie plate. Remove and discard skin from salmon; cut fillet into bite-size chunks. Place salmon pieces in large bowl and add thawed onions and their sauce, the peas, celery, tarragon, and black pepper, mixing well. When potatoes are cool enough to handle, cut into small cubes and add to salmon mixture. Spread mixture in pie plate.
In a small bowl, beat milk and egg to blend. Stir in baking mix and pecans just until moistened; do not over mix. Pour evenly over filling. Bake 22 – 25 minutes or until top is golden brown and filling bubbles. Cool 10 minutes before serving.
Nutrition information per serving: protein: 20g; fat: 20g; saturated fat: 3g; carbohydrate: 35g; fiber: 4g; sodium: 492 mg; cholesterol: 72 mg; calories: 399.