In saucepan, combine meat, onion, bouillon and water. Bring to boil, lower heat and simmer until very tender (about 1½ hours). Add more water as necessary to keep meat covered. Allow meat to cool in broth. When cool enough to handle, shred meat. Reserve 1 cup of broth.
In meantime, puree onion, red pepper and garlic in food processor.
In skillet heat oil on medium high. Add shredded meat and lightly brown. Add pureed vegetables, tomato sauce, Sazon, oregano, Adobo and reserved broth. Bring to boil, lower heat and simmer until mixture dries about 20 minutes.
Arrange meat, black beans, rice and plantain on platter and serve.