In a large bowl, add the instant noodles and cover with cold water. Let soak until slightly softened, about 5 minutes. Drain and set aside until ready to use.

Optional step: Make the shrimp stock. In a small saucepan, add the shrimp heads and shells, and cover with 2 cups water. Bring to a boil and simmer, uncovered, 15 minutes. Remove from heat and let cool a little. Transfer all the contents of the saucepan into a blender and blitz into a fine puree. Strain the stock, pressing on the pulp to squeeze out all the remaining liquid. You should have about 1 cup shrimp stock.

Prepare the sauce. In a medium sized bowl, add the oyster sauce, chili sauce, sweet soy sauce, and ketchup. Set aside until ready to use.

In a large skillet over medium high heat, add the oil or fat.

Add the garlic and cook, stirring, until fragrant, 30 seconds. Follow with the cili boh and cook, stirring, until all the liquid has evaporated.

Add the proteins and cook, stirring, until just cooked.

Sprinkle with the instant noodle seasoning.

Add the sauces, and stir to combine.

Pour in the stock if using, or 1 cup water.

Break an egg into the center of the mixture. Let cook undisturbed, until slightly set, about 30 seconds. Stir to incorporate.

Add the mustard greens stems and cook, until slightly softened, 1 minute.

Then, add the leaves and cook, stirring, until just wilted.

Finally, add the softened instant noodles and toss to thoroughly incorporate.

Serve immediately.