In a mixing bowl, add all the ingredients of sauce, mix well, do a taste test and adjust if needed. Set aside.
When tofu cubes are well sautéed, remove using a slotted spoon and set aside in a bowl.
In the same saucepan, if needed, add more oil (I did not) and celery; sauté on medium high, stirring often for a minute.
Add rest of the veggies – bell peppers and carrots; fry again, stirring continuously on high heat until slightly charred but still has a bite; about a minute or two.
Lower heat, simmer for a minute or so until the sauce is slightly thick and tofu and veggies have absorbed some of the sauce. Adjust consistency if needed (by adding a bit of water; not too much).