Place shrimp in a large bowl. Add Cajun seasoning and 1 tablespoon of the oil; toss to coat. Heat 1 tablespoon of the oil in a large skillet over medium-high. Add shrimp in an even layer; cook until browned on both sides but not fully cooked through, about 2 minutes total. Transfer shrimp to a large plate, and set aside.
Return skillet to medium; add remaining 1 tablespoon oil. Add snow peas, garlic, ginger, and white and light green parts of scallions; cook, stirring occasionally, until garlic and ginger are fragrant and snow peas are just tender-crisp, about 2 minutes. Add vinegar, and cook, stirring constantly, until almost fully reduced, about 1 minute. Reduce heat to low, and add butter, fish sauce, lime juice, and hot sauce, stirring until butter melts. Add shrimp; stir until coated in sauce and cooked through, about 2 minutes. Remove from heat; top with peanuts, cilantro, and dark green parts of scallions. Serve over rice.
