Stir together the soy sauce, lime juice, 1 tablespoon sugar, and 2 tablespoons water; set aside. Season shrimp with salt and pepper, and stir-fry in a hot nonstick skillet (or wok) with 1 tablespoon oil until pink. Transfer to a plate. Add remaining 1 tablespoon oil and garlic to wok; stir-fry 30 seconds. Add chard, and stir-fry until wilted. Season with salt and pepper; transfer to a platter. Pour in sauce mixture; boil 1 minute. Add shrimp; stir-fry until heated through. Spoon shrimp and sauce over greens.