Heat oil in a skillet over medium-high heat. Saute onion until translucent, about 2-3 minutes. Add the zucchini and tomato; cook until soft. Season with salt.
Add the tofu and chicken stock. Use larger amount of stock if you want the dish to be slightly soupy. Let it boil for 1 minute.
Drizzle the beaten egg over tofu mixture and let it cook until the eggs are set, Sprinkle with green onion and toasted sesame seeds. Season with salt and pepper if needed. Serve warm with rice.
Notes
Vegetarian adaptable: Us vegetable stock instead of chicken stock