In a large saucepan, cover the peas with water and bring to a boil. Simmer over moderately low heat until tender, about 40 minutes.
Add a generous pinch of salt and let stand for 5 minutes, then drain well.
Meanwhile, in a large saucepan, melt the butter. Add the onion, ginger, garlic and chile and cook over moderate heat, stirring occasionally, until softened and just starting to brown, about 10 minutes.
Add the berbere and turmeric and cook, stirring, until fragrant, about 2 minutes. Add the tomatoes and cook, stirring until softened, about 5 minutes.
Stir in the coconut milk and stock and bring to a boil. Simmer over moderately low heat, stirring occasionally, until the tomatoes break down and the sauce is thickened, about 20 minutes.
Add the peas to the sauce and cook over moderately low heat, stirring, until the peas are lightly coated, about 10 minutes. Fold in the cilantro and scallions and serve.