Place the beef broth and fish sauce into a sauce pot over high heat.
Once simmering, remove from heat and add green onion.
While the broth is heating, heat another small pot of water to a boil.
Once boiling, gently add the egg and cook for 5 minutes for a soft cooked egg.
Heat a cast iron skillet to high heat. Place the pork belly onto the hot skillet and sear on all sides until golden brown. Remove from heat and slice into 1/4 inch thick slices.
Drain the Miracle noodles vermicelli noodles, then add to the broth and stir to heat the noodles.
Place the broth with the noodles into a large bowl. Place 1/2 the slices of pork belly in the bowl. Peel the egg and slice in 1/2, then place into the bowl with yolk facing up.
Garnish with additional sliced green onion and slices lime if desired. Serve warm.