Open can of tomatoes and drain and discard between 1 and 2 cups of juice out of the can.
In a large mixing bowl, squish tomatoes with your hands (or cut with kitchen shears). Add chilis, onions and spices and pour half a blender full at a time into your blender. Pulse or puree until you reach your desired consistency.
This salsa tastes best when made a day in advance and chilled in the fridge before serving to let the flavors mix. Store in an airtight container for up to 3 days in the fridge.