Heat the oil in a large wok over high heat. When smoking hot, chuck in the garlic and red chilies and stir-fry 30 seconds, or until fragrant. Add the onion and stir-fry 1 minute, then tip in the scallops and stir-fry 1 to 2 minutes longer, or until the scallops start to turn golden at the edges.
Pour in the soy sauce and fish sauce and sprinkle in the sugar and black pepper. Mix well and stir-fry 1 minute, or until the scallops are just cooked through and tender.
Throw in the basil leaves, mix well and serve immediately. You can use scallop shells for presentation, if you like.