Combine all the ingredients for the guacamole in a bowl (or blender for a smoother version), and stir or blend until you reach the desired consistency.
Place the shrimp in a small amount of boiling water, with lemon juice and salt to taste. Cook for 45 seconds to a minute. Drain immediately, rinsing very well with cold water to stop the cooking.
To assemble, spoon about 1 tbsp of the guacamole into individual shot glasses.
Top with tomatoes and shrimp, equally divided among the shot glasses.