Just general measurements, there really isn't a right or wrong and add in any extra spices you're fond of.
One tomato, about the size of a baseball or 3/4 C chopped
1/4 C (heaping) onion, diced
1/4 C bell pepper, seeded and diced (I used red)
1 jalapeno, seeded and finely diced
1 Tblsp parsley or cilantro, finely chopped
1/2 lemon or lime, squeeze all the juice out
S&P to taste
-Mix, let sit for an hour-enjoy.