In large, deep skillet, heat 1/2-inch corn oil. Add prosciutto and cook until it turns dark brown and curls up on ends. Drain on paper towels. Cool and crumble into small bits.
For dressing, in medium mixing bowl, combine mustard, sugar, water, garlic, vinegar and salt. Whisk until combined. Whisk in oil in thin stream. Add pepper and oregano; whisk to combine. Adjust seasoning to taste, adding more sugar or garlic if necessary.
Place lettuce, onion, cheese and prosciutto in large bowl; toss. Add enough dressing to lightly coat leaves; toss and serve immediately.
Refrigerate extra dressing in airtight container for future use.Makes 4 Source: