PREPARE vegetables as directed.

In a skillet over medium heat, FRY chorizo, STIRRING to crumble, until almost done; POUR off any excess grease.

ADD vegetables, except tomatoes; SAUTE with chorizo until vegetables are softened; ADD tomatoes if desired; SET aside.

In a small mixing bowl, beat together eggs, milk, salt and pepper.

In a medium skillet over medium-high heat, MELT butter; TILT pan to coat bottom.

POUR eggs, all at once, into skillet; SLIDE skillet rapidly back and forth over heat, STIRRING lightly with a wooden spatula to spread egg mix over bottom of skillet as it cooks.

Let skillet rest briefly over heat while egg sets and bottom lightly browns--center should remain shiny; TILT pan, RUN spatula under edge of omelet; sharply jerk skillet to loosen omelet.

SPOON vegetables across center of omelet; use spatula to lift edge of omelet and fold edge to cover vegetables, leaving about 1/3 of omelet uncovered.

SLIDE omelet from pan onto plate; FOLD over remaining third.