Carefully wash the snails. Put them in a pot with cold water and bring to a boil. Cook for about 30 minutes. Halfway through, add the salt. When done, drain the snails and take off the end of the shell using a knife: this allows the snail meat to absorb the sauce and makes it easier to remove the snails from their shells. Meanwhile, pour ½ glass of oil in a pot, fry the chopped onion to a light brown and add chopped tomatoes. Cook for about 10 minutes, then add the snails, season with oregano and breadcrumbs. Cook for 5 minutes.