Hello Nycfem,
It might be a little bit more work but the end results I hope will be satisfactory to your taste.
You can use a heat tolerant oil to get the dish started and flavor it with a dash of sesame so it doesn't burn. To me sesame oil is more for flavoring the dish because it starts to burn so easily with the heat. When you cook the yellow onions especially in stir fry, onions sweat a lot so you might want to cook them first and get rid of all the access water from them.
It might be a good idea to marinade the tofu in the coconut milk and some basil to flavor it and add these three items at the end of the cooking process. (I do apologize, I have never cooked with tofu) I only say this because tofu I believe is a moist item and you don't want to dry it out.
The point of all of this is so your dish will not be full of moisture and you will taste every item in the dish and not taste just the sauce because it cooked all together, it tends to loose some flavor.
I hope this helps and don't forget to season, a bit of Himalayan salt and a dash of pepper
Bon Appetite!