Preheat oven to 400°F. Lightly oil 9 x 13 pyrex or casserole dish.
Add olive oil to a large pot and cook onions and garlic on a medium heat for 10 minutes. Add salt, pepper, marjoram, thyme, mushrooms and mustard. Cook about 5 more minutes.
Add sweet potato, white potato, carrots and stock. Bring to a boil. Reduce heat, cover and simmer until vegetables are fork tender (about 15 minutes).
Add dissolved cornstarch to thicken. Add peas, corn, tofu, soy sauce, and salt, stirring frequently.
Pour the vegetables/tofu mixture into the oil casserole dish.