In skillet set over medium heat, toast spices for 3 to 5 minutes, or until fragrant. Transfer to your Crockpot slow cooker.
Add onion, cut side down, and ginger to skillet. Increase heat to medium-high; cook for 8 to 10 minutes or until starting to char. Remove from skillet; set aside.
Heat oil in same skillet; cook short ribs for 8 to 10 minutes or until browned and slightly charred.
Smash garlic cloves with flat side of knife. Add to slow cooker, along with onion mixture, short ribs, soy sauce, brown sugar, and salt.
Pour in 6 cups of water, broth, and fish sauce; cover and cook on LOW 6 to 8 hours or on HIGH 3 to 4 hours, or until beef is very tender and broth is flavorful.
In cheesecloth-lined sieve, strain broth; reserve beef short ribs for another use. Skim extra oil from broth. Return to slow cooker. Cover; cook on HIGH 10 minutes.
Divide hot cooked noodles and sliced sirloin beef among 4 bowls. Pour hot broth over top (the heat of the broth with cook the beef slices).
Garnish with bean sprouts, green onions, basil, cilantro, and chili peppers. Serve with lime wedges.