Colombian Beef Rib Soup

Name: Colombian Beef Rib Soup
Cuisine: American, Latin American
Ingredients: 1 kg (2.2 lbs) beef short ribs, cut into 2-inch pieces; 8 cups water; 1 large white onion, finely chopped; 4 garlic cloves, minced; 3 medium potatoes, peeled and quartered; 2 green onions, chopped; 2 ears of corn, cut into thirds; 1 cup cilantro, finely chopped (divided); 2 tsp salt (adjust to taste); 1 tsp ground cumin; 1 tsp black pepper; White rice (optional); Lime wedges; Avocado slices