How closely did you follow that recipe?

I only ask because that recipe won’t work exactly as written and neither will most recipes you find online. The only websites I follow closely are Americas’s Test Kitchen and Serious Eats, even then, some tweaking might be involved.

This recipe lacks salt (outside of the soy sauce) and aromatics like garlic, ginger, and peanut oil.

I used to make bland stir fry until I finally figured out some things rules and they translate across cooking:

• Salt is important! Making noodles, rice, potatoes, beans, lentils, etc? Heavily salt the water. Salt meat before you cook it. Taste your dish while cooking it and add more salt if it needs it. Taste it before you serve it and add more if it needs it. Obviously, too much salt can be a problem but it’s still better than heavily processed foods.
• Sear all meat until it forms a browned layer. Look up the Malliard Reaction. It’s goes for veg too when roasting or frying.
• Fry aromatics like onions, garlic, ginger, and dried spices before adding anything else to the pot/pan.
• Taste the sauce before you use it. That sauce is okay but doesn’t seem like enough for that amount of food. Also, you’d be surprised how much sugar is in store bought and restaurant sauces. I don’t think the amount in this recipe is enough.
• Speaking of sauce, a very small amount of sesame or peanut oil can go a long way to enhancing a stir fry sauce. Worcestershire sauce also seems like a weird addition.