1. Combine the malagueta peppers in a food processor or blender, and process them until the mixture is a thick paste.
2. Gradually add half of the onion and half of the garlic and continue to process, scraping the sides of the container to blend all ingredients into the paste. Add the lemon juice and process again to mix.
3. Transfer the sauce to a glass bowl, cover with wrap, and allow the mixture to stand for 30 minutes.
4. In a large heavy skillet, heat the olive oil over medium heat. Add the remaining onion and garlic. Saute for 2 minutes, add the chayote or summer squash, and continue to saute, stirring occasionally, for about 5 minutes.
5. Add the red and green bell peppers and allow to cook for another 5 minutes. Add the black pepper and remove the pan from the heat.
6. Place the sauteed vegetables in the refrigerator and chill for 2 hours.
7. When ready to serve, arrange the vegetables on a large platter and drizzle with a small amount of sauce. Sprinkle with the chopped tomato for added color. Add additional black pepper as desired.

Note: Malagueta peppers are a pickled hot pepper used in traditional Brazilian cooking. They can be found in some Latin American markets