There are two ways of doing this - the slow (and cheap) way, with dried beans, or the quick (and relatively expensive) way with tinned beans. Using dried beans probably results in a more nutritious salad with a better texture. If you want to add green beans, why not stick with the healthy approach and use fresh ones.
Let's start with the preparation of the dried beans and the fresh green beans, as once these are cooked the process is the same as for the tinned stuff. It should be possible to buy a bag of mixed dried beans in your local health food shop. Otherwise mix together a handful each of kidney beans, borlotti beans, flagollettes etc. Go for an interesting colour combination. Rinse the beans and leave to soak overnight. When planning how much salad to make and what size of pot to soak the beans in, note that they will swell to at least twice their size after soaking. This is about as much attention as you need to give to measurement with this recipe.
To cook the beans, rinse, put in a large pot and add water to cover by about five centimetres (no salt). Bring to the boil and boil vigorously for ten minutes then reduce to a simmer. They should take another half hour or so to cook - taste them to see if they are soft enough and if they are, rinse in cold water.
Okay, how about the green beans? These come in all shapes and sizes - fine beans, French beans, flat beans - and they're not all green either. Use any kind. To cook, top and tail them (that means cutting off a little bit at each end and throwing it away), cut into 4 or 5 centimetre pieces and throw into a pan of boiling water with a pinch of salt added, for about 8 minutes (less for fine beans, longer for flat beans). Rinse in cold water.
Onto the salad...
Beans, rinsed and drained
1 small, or 1/2 large onion, finely chopped
3 or 4 cloves of garlic, chopped
2 or 3 fresh tomatoes, chopped
Olive oil
2 or three tsps. of lemon juice or vinegar
1 bunch of green coriander, chopped
1 level tsp. whole cumin seed, roasted and pounded or 1/2 tsp. cumin
powder
Salt to taste
Mix everything together except the olive oil. Add it last and stir gently. Use enough oil to coat everything nicely but not so much as to make a big puddle at the bottom of the bowl.
This salad, like most, tastes much better after a few hours in the fridge and it will keep for 2 or 3 days. Stir again before serving,