Place the beef stew meat, onion, red bell peppers, carrots, garlic, and ginger in the slow cooker.
In a separate bowl, whisk together the red curry paste, coconut milk, beef broth, fish sauce, and brown sugar until smooth.
Pour the curry mixture over the beef and vegetables in the slow cooker. Stir gently to combine.
Cover and cook on low for 7 to 8 hours, until the beef is tender and the vegetables are soft.
Stir in the lime juice right before serving.
Ladle the soup into bowls and top with fresh cilantro. Serve with lime wedges on the side.