Place potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain and set aside to cool slightly.
Heat olive oil in a skillet over medium heat. Cook onion until tender, about 10 minutes.
Bring a small saucepan of water to a boil. Boil chile peppers until soft, about 5 minutes. Run chiles under cold water to cool until cool enough to handle; remove and discard skins.
Blend onion, chile peppers, cheese, vegetable oil, garlic, salt, and pepper in a blender until smooth. Stream evaporated milk into the blended mixture while continuing to blend until a creamy sauce is achieved.
Arrange 1 lettuce leaf onto each of 8 plates. Halve potatoes and arrange 3 halves onto each lettuce leaf. Drizzle creamy sauce over the potatoes. Top each with an egg half and two black olive halves.