Begin by slicing the beef and placing it in a large plastic bag.
Whisk curry paste, onion, milk, and ginger together in a bowl and then pour mixture into the plastic bag, evenly coating the beef. Seal the bag shut and allow the beef to marinate for anywhere from 10 minutes to 2 hours. The longer you marinate it the more flavorful it will be, but if you're lazy and impatient like me, 10 minutes will do the trick!
Once beef has marinated, heat oil into a large skillet and use kitchen tongs to remove the beef and place it onto the skillet. Pan fry the beef on all sides until it's cooked on the outside.
Reduce heat to a simmer, pour the curry sauce into the skillet, add the red pepper slices and cover the skillet with a lid. Cook for 10-15 minutes or until beef is cooked to your desired liking (if it's taking too long, you can always bring the heat up to medium).
While the beef is cooking, cook the cauliflower rice in a separate skillet with a dash of oil and water.
To serve: pour cauliflower rice into a bowl or on a plate and top it with beef, red peppers, curry sauce, and some cilantro.