In a medium bowl, whisk together vegetable broth, soy sauce, brown sugar, and sesame oil until well blended, about 1-2 minutes.

Heat a large skillet or wok over medium heat and add a tablespoon of oil. Once the oil shimmers, add sliced carrots and sauté for 3-4 minutes until they begin to turn golden and slightly tender.

In the same skillet, add another tablespoon of oil if necessary, then toss in chopped onions. Sauté for about 2 minutes until they turn translucent, then add broccoli florets.

Add a little more oil to the skillet if needed, and then add the sliced red bell peppers. Sauté for about 2-3 minutes until they soften.

Bring back the sautéed veggies and add the cooked lo mein noodles to the skillet. Pour the prepared sauce over the noodles, tossing everything together gently.

Once everything is well combined and hot, pour the Veggie Lo Mein into serving bowls. Garnish with sesame seeds or chopped green onions.