Place the beef, quartered onion, water, salt, and pepper in a Dutch oven. Bring to a boil, cover, and simmer gently for 2 to 2 1/2 hours until the beef falls apart.
Transfer the beef to a bowl. Discard the onion, reserve the broth, and shred or pound the beef until finely separated.
Return the beef to the pot with 1 cup of reserved broth. Simmer uncovered for 10 minutes until moist and concentrated.
Make the Bogobe:
Bring 3 cups of the water and the salt to a boil. Whisk the sorghum meal with the remaining 1 cup cold water, then slowly whisk it into the pot.
Reduce the heat and cook for 20 to 25 minutes, stirring often, until thick and smooth.
Cook the Greens:
Heat the oil in a skillet. Cook the chopped onion for 5 minutes, add the greens and salt, and sauté for 8 to 10 minutes until tender.
Serve the seswaa with hot bogobe and greens.
Notes
Add hot water during simmering if the beef begins to dry out.
Sorghum meal thickens as it stands; loosen bogobe with a splash of hot water before serving if needed.