In 8-quart saucepot over high heat, heat unpeeled potatoes and enough water to cover to boiling. Reduce heat to low; cover, simmer 25 to 30 minutes, until potatoes are fork-tender.
Meanwhile, in large bowl, with wire whisk or fork, mix salad oil, vinegar, salt, and pepper.
When potatoes are done, drain; cool potatoes until easy to handle. Peel; cut potatoes into 1/8"-thick slices. Thinly slice pears. Add potatoes and pears to dressing; toss gently until well coated.
Line salad bowl with lettuce leaves; spoon mixture onto lettuce. Serve warm. Or cover and refrigerate to serve chilled later.