Once your protein and vegetables are nearly done, add the cooked noodles to the pan. Toss everything together, then remove from heat before adding chili oil. This prevents the oil from breaking down while ensuring even distribution.
Start with less chili oil than you think you need you can always add more. Toss thoroughly, allowing the noodles to absorb the oil and flavors. The residual heat will warm the chili oil sufficiently to release its aromatics without destroying delicate compounds.
Taste and adjust seasoning with soy sauce, vinegar, or additional chili oil as needed. The final dish should balance heat, salt, acid, and umami in harmony.