[Blarg]

Using the higher smoking point oil, per Born 2 Loose's suggestion, is a good idea.

It sounds to me like your meat just heated through in the slow normal way without getting any caramelization. Stir frying is supposed to be done with a really hot pan. That helps get the carmelization going too, which adds a huge amount of flavor. Either sugar or salt tossed in can help caramelization of the meat/veggies too.

I also wonder if you cooked the onions a little too long. If they have a little more crispness to the bite, they will usually have a little more flavor, too.

Maybe doing everything faster and hotter will help.

And a little marinating can be cool too.

Finally, when food is bland, adding some heat, as in peppers or hot sauce, wakes up the taste a lot and makes even dull food more palatable.