Season the beef with 1 teaspoon salt and the pepper. Heat the oil in a Dutch oven and brown the beef in batches, then set it aside.
Cook the onions for 8 minutes. Add tomatoes, garlic, ginger, curry powder, and cumin; cook for 6 minutes until the tomatoes soften.
Braise:
Return the beef and add 2 cups stock. Cover and simmer gently for 45 minutes until the beef begins to tenderize.
Add the green banana pieces, remaining stock, and remaining salt. Cover and simmer for 25 to 30 minutes, turning the pieces gently once, until the bananas are tender and the beef is soft.
Finish:
Mash two or three banana pieces against the side of the pot to thicken the sauce. Fold them back in gently, adjust seasoning, and finish with coriander.
Notes
Green East African cooking bananas are starchier and less sweet than dessert bananas; green plantains are the closest substitute.
Avoid vigorous stirring after adding the bananas so the pieces remain distinct.