Replace your homemade sauce (soy, mirin, brown sugar etc.) with about 5–6 tbsp of a good quality teriyaki sauce.

You’ll still want to divide it:
Use about 1–2 tbsp to marinate the salmon.
Use the remaining 3–4 tbsp to toss through the noodles and veg at the end.
If it’s very thick, you can loosen it with a splash of hot water when tossing through the noodles.

Shop bought sauces vary in sweetness & saltiness. Taste yours before adding more soy sauce or salt to the stir fry. If you still want a little depth, you could add a dash of rice vinegar or a squeeze of lime at the end to brighten it up.