For the veggies: I typically do sweet red peppers sliced into rings, and green beans cut in half or thirds (about a heaping cup of each).
Other veggie options: Fresh spinach would also be great (hardly needs any cooking time – only about 1 minute, so add right at the end). Frozen mixed veggies would also work (don’t need much cooking time here, either – probably 4-5 minutes).
More flavor: Adding a bit of lemongrass or lime to the sauce is also bright and delicious! I didn’t want to get too carried away with the ingredients so left it out, but if you have some, go ahead and add it!