Pat the London broil dry
Season both sides with salt, pepper, garlic powder, and onion powder
Optional: sear in a hot skillet for 2 to 3 minutes per side
Place sliced onions and minced garlic in the bottom of the crock pot
Add the London broil on top
Pour in 1 to 2 cups of beef broth
Add Worcestershire sauce and optional soy sauce
Add optional carrots, potatoes, or mushrooms
Cover and cook on low for 7 to 8 hours or on high for 4 to 5 hours
Check for tenderness with a fork
Remove the meat and let it rest for 10 minutes
Slice thinly against the grain
Serve with the cooking juices or thicken them into gravy