In a small pot, boil the potatoes in water until fork-tender. Drain and cool.
Toast the guajillo chilis in a dry frying pan until pliable.
Boil in 4 cups of water until tender and scoop out one cup of the chili water.
In a blender, mix the chilis, chili water, chipotle pepper, tomatoes, onions, garlic, and ¼ cup of cilantro until smooth.
Pour the sauce in a frying pan and simmer for 15 minutes. Add the cactus at the end just to warm through, about 2 minutes.
Mash the potatoes with a fork and mix in the eggs one at a time. Add the shrimp, ¼ cup of cilantro, salt and pepper, and stir to combine.
Using a ¼ cup measure, pan fry the shrimp cakes in oil until golden brown, about 3 minutes per side or until golden brown. Gently flip the cakes as they are delicate.
Drain the cakes on a paper towel and then plate with the sauce.