Toss tomato, avocado and cilantro together in a small bowl.

Season with salt and pepper. Set aside.

Beat eggs in a separate small bowl just until whites and yolks are combined, not long enough to become frothy.

Over medium-high heat, melt butter in a 6- or 8-inch skillet (preferably slope-sided and non-stick) until bubbling but not brown.

Tilt skillet to spread butter evenly around and up sides.

Pour eggs into the hot skillet, tilting and shaking the pan gently with one hand while stirring eggs briskly with the flat of a fork.

Tilt pan and lift edges of omelet with a fork to allow runny egg to reach sides and cook.

When eggs begin to firm up and there is almost no runny egg left, add shrimp and cheese, spreading them over the center third of the omelet.

Immediately use the fork to fold each side of omelet up over center filling.

Tilt the pan to help roll omelet into a loose cylinder.

Cook 10 to 30 seconds longer, depending on how brown you prefer the bottom (check for brownness by lifting a corner).

Slide omelet onto a warmed plate, top with tomato-avocado mixture and serve.