1. Cut the bell peppers into small pieces. Fry them over low heat until they are almost cooked.
2. Meanwhile, also cut the onions into small pieces. Cook them.
3. Once they are almost cooked, add them to the bell peppers and continue cooking over low heat.
4. Season with salt and pepper, then add cayenne pepper to taste.
5. Cut the chicken into small pieces.
6. Remove the bell peppers and onions from the heat.
7. Cook the chicken.
8. Once cooked, add the juice of one lemon, as well as the onions and bell peppers. Let it simmer over low heat for a few moments, then turn off the heat.
9. When serving, reheat the chicken. Cut the tomatoes into small cubes. To garnish the fajitas: spread sour cream on the tortilla, add guacamole, some tomato cubes, and a few small pieces of lettuce. Add the chicken filling, roll it up, and enjoy!