Clean, chop, and prepare vegetables and protein. You can follow the vegetables I've listed for this recipe or whatever vegetables you have or prefer. However, total you should have about 7 cups of vegetables and 3 cups of protein. Your vegetables should be about double the amount of proteins you use. Try to cut vegetables and proteins into equal bite-sized pieces. Set aside.
In a bowl, mix oyster sauce, soy sauce, fish sauce, sesame oil, sugar, white pepper, and chicken bouillon. In a separate small bowl, add cornstarch with water to make thickening slurry. Set aside.
In a large frying pan or wok, heat up 4-5 tablespoons of cooking oil using medium-high heat. Add in minced garlic and stir fry until fragrant (about 1 minute). Add in chicken or whatever protein you are using to the wok. Season chicken with a sprinkle of salt and white pepper. Stir fry until chicken is ready (about 5 minutes).
Add in mushrooms and fishballs. Cook for another 3 minutes or until cooked.
Add in ginger pieces, onions, and green onions. Stir fry for 30 seconds.
Add in cabbage, broccoli, and squash. Stir fry for 30 seconds.
Add in sauce mixture and mix everything together. Add in about 3 cups of water or just enough water to fill the pan below the top of your vegetables and protein (just barely covering the ingredients). Bring to a boil.
Add cornstarch and water slurry. Mix everything together and continue cooking until desired tenderness of vegetables (about 3 minutes). Serve chop suey with a bowl of hot rice or with crispy noodles!