In a wok, heat the oil over high heat until smoking. Add the chiles and salt; stir-fry until browned, 45 seconds. Add the onion, ginger and garlic; stir-fry until fragrant, 15 seconds. Add the peppers and cook until crisp-tender, 30 seconds. Add the shrimp and stir-fry until nearly cooked through, about 5 minutes. Stir the sauce, add to the wok and cook until thickened slightly, 30 seconds. Stir in the cashews and sesame oil; serve.