Vietnamese thịt bò xào khoai tây is something of a fusion stir-fry, one that combines beef with Western vegetables, namely potatoes (khoai tây in Vietnamese) that typically are deep-fried until crisp. This recipe is a potato-free riff on that dish, and it derives loads of depth, savoriness and umami from garlic, fish sauce, soy sauce and tomatoes. We leave the seeds in the chilies for noticeable but not scorching heat; feel free to remove them to tone down the spiciness. If you wish to stay true to the inspiration stir-fry, serve this atop french fries, either homemade or frozen. Otherwise, steamed jasmine rice is a fine accompaniment, or you could double down on the carbs and serve both potatoes and rice.