Sweet and Sour Seashells

1 lb uncooked small seashell pasta (9 C cooked)
2 Tbsp vegetable oil
3/4 C sugar
1/2 C cider vinegar
1/2 C wine vinegar
1/2 C water
3 Tbsp prepared mustard
to taste black pepper
1 jar (2 oz) sliced pimentos
2 small cucumbers
2 small onions, thinly sliced
18 leaves lettuce