Ree Drummond's pico de gallo from Food Network is a good recipe made with onions and tomatoes. It calls for other fresh ingredients and has many positive reviews from home cooks who have tried it, as of 2015.
To make pico de gallo, dice approximately three onions and 12 tomatoes. There should be roughly the same amount of each ingredient once they have been diced. You can use red or yellow onions and your choice of tomatoes, though Roma tomatoes are suggested for this recipe. Roughly chop about 2 cups of fresh cilantro leaves. Slice one or two jalapeños in half, removing the seeds and white membranes. You can leave some of the membrane if you want the dish to be extra spicy. Next, dice the jalapeños very finely.
Add all of these ingredients to a bowl. Squeeze the juice form 1/2 of a lime over the top of the ingredients in the bowl. Sprinkle some salt over the top, then stir to combine. Taste the pico de gallo and add more salt, jalapeño or lime juice to taste before serving.
This recipe has several positive reviews, as of 2015. Many people wrote that this dish is easy to make and is very flavorful. One reviewer suggested using hot sauce in place of jalapeños if they are not available.