Preheat Blackstone griddle to medium-high heat. Drizzle vegetable oil then add the onion, bell pepper, mushrooms, chicken, and broccoli slaw. Cook for 10-15 minutes until the vegetables are tender and the chicken is fully cooked. Season with salt and pepper.
Add the noodles and garlic to the griddle. Mix and cook for 2 minutes until the garlic is fragrant.
Sprinkle the brown sugar and pour the teriyaki sauce over the top of the lo mein. Stir with spatulas until a sauce is created coating the lo mein. Remove from the griddle and place on a large serving plate. Top with sesame seeds if using. Serve immediately.
