Heat 1 tbsp. oil in a large frying pan over medium heat. Add shallot and garlic and cook, stirring, until shallot begins to soften, about 3 minutes. Stir in red curry paste and cook, stirring, 45 seconds. Add beef and salt, breaking beef into small pieces with a wooden spoon. Cook, stirring occasionally, until beef is just cooked through, about 5 minutes.
Add coconut milk and sugar, reduce heat to medium-low, and cook until most of liquid is absorbed, about 8 minutes, stirring occasionally.
Meanwhile, make slaw: In a medium bowl, combine cabbage, green onions, cilantro, remaining 2 tbsp. oil, and 1 tbsp. lime juice. Toss to coat, then season to taste with salt and pepper.
Remove beef from heat and stir in remaining 2 tsp. lime juice. Make sandwiches with beef mixture and slaw.
*Find in the Asian aisle of most grocery stores.