Cut halibut filet into 4 pieces (8-ounce portions). Lightly salt and pepper.
Empty contents of mashed potatoes package on large plate. Coat filets liberally, gently pushing potatoes into filets. In large sauté pan, preheat a generous amount of canola oil, on medium heat.
When oil is hot, gently place the halibut in pan, being careful not to splash. Sauté fish until golden brown (approximately 2-4 minutes). Turn filets and reduce heat to medium-low.
Cover pan and let sauté until done (until flaky, or approximately 8-12 minutes). Remove from heat. Add lemon juice to taste and serve.