Add all but about ¾ cup of the shrimp to a food processor fitted with the blade attachment. Turn it on to pulse it just a bit. Then add the egg and cilantro and blend again until it's smooth, about 10 seconds. Add this to a mixing bowl and set aside.
Roughly chop the remaining ¾ cup of shrimp into small pieces. Add them to the smooth portion in the mixing bowl, along with the salt, cumin and pepper. Mix just to blend and set aside.
Coat the bottom of a large sauté pan with olive oil and place it over medium-high heat. Once it's very hot, use a ½ cup measure to scoop and shape the shrimp mixture into 4 burgers. They will be sticky, but will easily hold together when you place them in the pan. Sauté them just until they're cooked through, 2 to 3 minutes per side. They should be golden brown.
Now add about 1 tablespoon or so of the guacamole to each half of the toasted buns. Add a burger to each, followed by a couple of tomato slices and a bit of the lettuce. Close the burger and enjoy! (These are best when the burgers are still warm.)