This is an irregular verb. It follows the conjugation pattern of the verbs abrazar and volar.
PresentPresente
Nosotros almorzamos en casa los domingos.
We have lunch at home on Sundays.
PreteritePretérito indefinido
Ayer almorcé con mis compañeros de trabajo.
Yesterday I had lunch with my coworkers.
ImperfectPretérito imperfecto
En la escuela almorzábamos a las doce.
At school we used to have lunch at twelve.