2 tablespoons peanut oil
1 red onion, chopped
2 cloves garlic, minced
2 tablespoons chopped fresh ginger
1 pound chicken, cut into chunks (optional)
1 tablespoon crushed red pepper, or to taste
salt and ground black pepper to taste
5 cups chicken stock
3 small sweet potatoes cut into chunks
1 (16 ounce) can chopped tomatoes, with liquid