Put the tomatoes in boiling water and wait 20 seconds or so. Take out the tomatoes, peel and discard the seeds, and put the flesh and juice in a bowl.
Cut the red pepper in half and cut out the pith, discard one of the halves and the pith. Cut into one inch/2cm strips and then into fine dice. Cut the three chillis in half lengthwise, cut off the stalk, discard the seeds and cut into fine dice. Wash your hands.
Soften the red pepper and chilli in a tablespoonful of olive oil over a medium heat for a few minutes. Add the tomatoes and juice and cook over a medium heat uncovered mashing with a wooden spoon from time to time, until it is like a sauce. Take off the heat, pour into a blender, blitz a couple of times, pour back in the saucepan and season with salt.
Take the scales off the tails of the crevettes and lightly season with salt. Chop the coriander to deliver a couple of good heaped tablespoonfuls.
Lightly saute the crevettes in a splash of olive oil both sides for a couple of minutes until coloured. Meanwhile reheat the chilli sauce if necessary and stir in the chopped coriander. Put the crevettes on to serving plates, spoon over a little sauce and serve.