Soak millet, corn couscous, and fonio in separate bowls of water for 20 minutes and drain.
Par-boil quinoa for 10 minutes if using as a substitute and drain thoroughly.
Steam all grains together for 20 minutes until cooked through.
Stir in the butter and remove the grains from the heat.
Brown the beef chunks in oil within a pan.
Add tomato purée, passata, water, salt, and pepper to the beef.
Add chopped vegetables and garlic to the pan after 10 minutes of simmering.
Simmer for 15 minutes until the sauce thickens and vegetables are firm.
Serve the steamed couscous topped with the beef and vegetable sauce.