Heat olive oil in a large wok or frying pan over medium heat. Add tofu, garlic and about half of the oyster sauce. Stir and cook for about 5 minutes, until garlic is lightly browned but not burning. Remove from the frying pan to a bowl, and set aside.
Add the frozen vegetables to the same frying pan and cook according to package directions, substituting stock for the water, and seasoning with the remaining oyster sauce.
When vegetables are cooked, mix the tofu garlic mixture back into the pan, and heat through. Serve plain or over rice.