Heat the oil in a skillet over medium-high heat. Add the carrot, celery, and onion. Cook about 4 min. Add garlic and cook about 30 s.
Add the buckwheat, pepper, hot broth. Cover and bring to a boil. Reduce the heat to low and simmer.
After 5 min., add the zucchini and simmer about 10 min.
Garnish with black pepper, sea salt. Add tomato, soy sauce and stir.
*if you use broth cube: 2 1/2 c of hot water combine with 1/2 broth cube