Someone once told me pico de gallo should have equal parts red, white and green, the colors of the Mexican flag. These measures will get you close. When you are done, adjust it according to whatever your eyeballs or taste buds tell you.
4 medium Campari tomatoes, diced
1/2 yellow onion, diced
1 jalapeno, diced
1/4 green bell pepper, diced
1/4 cup cilantro, diced
2 limes, juiced
1/2 tsp sea salt
Mix tomatoes, onion, jalapeno, bell pepper, cilantro, lime juice and salt in a non-reactive bowl.
It's best to mix your pico de gallo in non-reactive bowl made of glass, plastic, stainless steel or ceramic. Except for stainless steel, metal bowls may react to the acid in citrus or tomatoes and impart a metallic taste to the food.