Dice the onion really small and add the lemon juice. Add the avocados, cut them in half and, with a fork, mash them with the onions. Dice the tomatoes and add them to the onions and avocados, cut the cilantro really small and add it to the mixture. Finally, add salt to taste and mix with a fork mashing the avocados so you have a nice texture. If you like, add the chilies. When it's ready (taste for salt) add the pits of the avocados so it won't turn black. Serve with tortilla chips and enjoy! (DO NOT EAT THE PITS)