Bring a large pot of water to a boil. Wash and dry produce.

Cut broccoli into bite-size pieces if necessary. Trim and thinly slice scallions, separating whites from greens. Roughly chop cashews.

Heat a large drizzle of oil in a large pan over medium-high heat. Add broccoli; season with salt and pepper. Cook, stirring frequently, until browned and tender, 4-7 minutes.

Add scallion whites, carrots, and garlic powder. (TIP: If pan seems dry, add a drizzle of oil.) Cook, stirring frequently and lowering heat if browning too quickly, until veggies are just tender and fragrant, 1-2 minutes more.

While veggies cook, in a small bowl, combine chili sauce, onion paste, half the vinegar, half the soy sauce, and ¼ cup water (all the vinegar, all the soy sauce, and ½ cup water for 4 servings).

Once water is boiling, add noodles to pot. Cook, stirring occasionally, until al dente, 5-7 minutes.

Drain noodles, shaking off any excess water, and transfer to pan with veggies. Add soy-chili mixture, half the cashews, and 1 TBSP butter (2 TBSP for 4). Toss until butter has melted and noodles are thoroughly coated, 30-60 seconds. Taste and season with salt and pepper if desired.

Divide lo mein between shallow bowls; garnish with scallion greens and remaining cashews. Serve.