NOTE: I don't really follow a set recipe for pico de gallo. It is one of those things that I believe you can't really mess up. You can adjust the heat or flavor to your liking. I usually base my recipe with what I have on hand. Here is a general recipe of quantities, but like I said you can really use more or less of everything and it will still be delicious with garden fresh tomatoes. I put it on top of everything, great garnish.
6 medium Tomatoes diced
1 medium Onion finely diced (Red, Yellow, or use a bunch of green onions, or any combination of the three)
1/4 cup fresh Cilantro chopped (I usually put a lot)
2 to 4 Fresh serrano or jalapeño seeded and minced (I leave these out for the kids or add a little bit of El Tapatio Mexican Hot Sauce)
garlic powder to taste
Salt to taste
Juice from one lime (sometimes I just don't have one and use a little bit of lemon juice concentrate or nothing).
Put all ingredients in a bowl and chill to allow flavors to blend.