Squeeze ½ of lime over shrimp and rinse. Heat canola oil in a large frying pan over medium heat. Add thyme and pepper, heat for 1 minute. Add garlic and shrimp, stir. Cook for 3 minutes then turn shrimp. Add butter and salt, cook for an additional 2 minute. Squeeze the other half of lime over the shrimp, remove from heat. Sprinkle with scallion to garnish.