Fill a large pot of water with hot tap water and add rice noodles. Allow noodles to soak for ~30 minutes to soften them.
Combine sweet soy, oyster sauce, regular soy sauce, rice vinegar, sirracha, sugar and garlic in a small bowl and stir to combine.
Heat wok on high heat and add 1 TBSP peanut oil.
Add prawns (if using) and stir fry for ~3 minutes until they are nearly cooked through.
Move prawns to the sides of the wok and add egg and cook for another 1-2 minutes.
Push egg to the sides of the wok with the prawns and add softened rice noodles and sauce.
Stir-fry noodles until most of the liquid from the sauce is gone.
Add broccolini and cook until tender crisp (about 2 more minutes). During this time let noodles sit and develop a bit of char on them.
Once broccolini is done, serve immediately.