In a food processor blend half of the onion, a quarter of the bell pepper, oregano, garlic, a pinch of pepper and a teaspoon of salt.
Cut the meat into a tube by inserting the knife lengthwise (in the same direction of the fibers). Season the meat inside and out with the blended mix. Stuff the beef with the longaniza, some onion strips, some bell pepper strip and some carrot strips. Marinate covered in the refrigerator for at least an hour.
After the hour has passed, heat the oil in a large heavy-bottomed pot (6 qt [6 lt] over high heat. Remove the meat from the marinade, reserve the marinade for later use. Pat dry the meat with a paper towel. Place the , in the heated oil, carefully to avoid burning yourself. Brown the meat, turning every few minutes to get a uniform brown color all over.
While the meat browns, mix water, tomato sauce, flour, and the remaining marinade. Remove the meat from the pot and pour in the tomato sauce mixture into the pot, stirring to incorporate all the browned bits. Stir in the olives, capers and the remaining carrot, bell peppers, and onion. Place the meat back into the pot.
Lower the heat to a minimum, cover with a tight-fitting lid and simmer for 1 ½ hours, rotating the meat every half hour so it cooks uniformly. The sauce should have been reduced to half, if it is too dry, add additional water.
Once this time has passed, remove the meat from the sauce, place on a cutting board and cut into slices, being careful not to burn yourself. Season the sauce with salt and pepper to taste. Pour the sauce into a serving plate and place the slices on top. Sprinkle with parsley.