Process onions and 2 tablespoons water in a food processor until very finely chopped, about 15 seconds, stopping to scrape down sides of bowl as needed.

Heat 1/4 cup niter kibbeh in a large Dutch oven over medium-high. Add onion mixture; cook, stirring often, until onion starts to stick to bottom of Dutch oven, about 15 minutes. Reduce heat to medium-low. Add remaining 1/4 cup niter kibbeh, and cook, stirring occasionally, until onion is meltingly tender and begins to fry and brown, about 15 minutes, adding additional niter kibbeh, 1 tablespoon at a time, if mixture looks dry.

Add bell pepper, garlic, and ginger to Dutch oven; cook, stirring often, until slightly softened, about 2 minutes. Add ground chicken and salt; stir vigorously using a whisk to break meat into small crumbles. Cook over medium-low, stirring occasionally, until meat is cooked through but not browned, about 5 minutes.

Add tomato paste, berbere, garlic powder, and onion powder to Dutch oven; cook, stirring constantly, until fragrant, about 2 minutes. Stir in chicken stock and diced tomatoes. Reduce heat to low; simmer, stirring occasionally, until chili is slightly thickened and flavors meld, about 30 minutes.

Divide chili evenly among bowls; garnish with feta cheese, fried onions, and scallions. Serve hot with injera or cornbread.