In a deep nonstick skillet set over moderate heat, warm the oil until it is hot.
Add the mustard and cumin seeds, and cook, stirring, 1-minute. Add the gingerroot and garlic, and cook, stirring, 1 minute more. Add the onion and green bell pepper to the seasonings and cook, stirring occasionally, for 5 minutes.
Add the green beans, tomatoes, and salt, and cook, stirring occasionally, for 5 minutes more. Add the water, bouillon cube, and salt, to taste. Bring to a boil, stirring, and add cous cous. Simmer, stirring occasionally, for 5 to 10 minutes, or until liquid is absorbed. Remove from heat, cover, and let stand 5 minutes. Before serving, stir in lemon juice and cilantro.