Squeeze the lime and divide the juice in two bowls or about the same quantity.
Remove the skin and pit from the avocados and add them to a bowl. Mash them with a fork.
Peel and mince the shallot. Add the minced shallot to one of the two lime juice bowl. Soak in lime juice for 10 minutes.
Seed the chili pepper and mince it. Cut the tomatoes in quarters and remove the seedy pulp. Mince the flesh into bits that are about the same size as the chili pepper and shallot bits.
Separate the cilantro leaves from the stems and discard stems. Finely mince the leaves and add them to the avocado mash. If using frozen cilantro, take about 1 1/2 tsp of frozen minced leaves.
Drain the lime juice from the shallot and add the soaked shallot to the avocado bowl. Add also the minced chili pepper and tomatoes.
Give the mixture a stir and add salt and lime juice (the fresh juice from the clean bowl, not the one where the onion had been soaking) to taste. Mix well before serving in order to properly season the whole mixture.
Add extra cilantro leaves as garnish (optional).