In a dutch oven or saute pan brown/cook through your chorizo.
Transfer the chorizo to a bowl or plate with a paper towel on it to absorb some of the grease.
In the same pan, saute onions until translucent (3-4 minutes).
Add the can of fire roasted tomatoes, salt, pepper, cooked chorizo and heat through.
Allow to simmer for 2-3 minutes.
Serve hot!