Peel onion and chop finely. Chop tomatoes and add
to onion mixture. Finely chop Serrano (or Jalapeno)
peppers and add to onion and tomatoes. (Be advised
that the pepper seeds themselves can be very hot.
Adjust to personal taste.) Rinse cilantro well,
then place on paper towel and gently squeeze dry.
Chop, and add to mixture. Stir everything well,
cover with wrap, and place in refrigerator. Juice
will accumulate as mixture sits, so stir occasionally.
Serve as you would salsa -- with chips, over fish,
on top of a baked potato...whatever suits your
fancy.