Sauté your yellow onions in oil until translucent and then add in your green onions and garlic
Continue cooking for about another minute, and then add in all of your sauces and spices and simmer for ~3 minutes on low heat.
Add in your cornstarch and mix well with the sauce, and then add your water and leftover veggie broth.
Add in your serrano chili (finely chopped). Note: feel free to sauté the chilies earlier in the recipe after you added the garlic! I tried this method this time for a change and I enjoyed the result, but both methods work well).
Simmer the mixture on low-medium heat for about 10 minutes until the sauce thickens well.
Add in your veg manchurian balls and cook for a couple of minutes in the sauce before serving.