Saute onion in a large skillet adding garlic and cilantro during the last minute or two.
Add meat and seasonings and stir well. Allow to saute for a minute or two, letting the meat absorb some of the flavors.
When it seems that it is really dry and the mixture is starting to stick add the tomatoes and liquid and scrape all the browned bits from the bottom. TONS of flavor there. Add sugar if using. ( The sugar makes the tomatoes taste more like home grown and home canned or even organic).
Reduce heat to simmer and cook for 20 minutes or so. When you are ready to use the mixture return heat to high and cook off almost all the liquid so that your filling is not runny or wet.