Heat the grill or a griddle pan to medium-high. Brush the corn with little oil, then grill for about 10 minutes, turning regularly until the kernels are tender and charred.
Let it cool, then remove the kernels off the cobs by using a sharp knife (stand it firmly on a chopping board and run the knife downwards).
Meanwhile, thinly slice the onion and garlic and halve the tomatoes.
Heat the remaining oil in a frying pan and sauté the onion. When soft, add the garlic and tomatoes. Cook for a couple of minutes, then add the spices and stir for a minute. Add the lime juice and a splash of water. Season with salt and pepper.
Sautee until the tomatoes are tender. Add the drained beans and cook until there is very little sauce left in the pan.
Serve warm with coriander leaves scattered on tip and a squeeze of lime juice.