If you're going for all medals, you'll get this eventually, as many medals require you to score over 2 million in a level. If you're impatient, a good level to get this on is Level 4-alpha. This is one of the easier Survival levels to score 2 million points on.
Make sure you've unlocked the UFO upgrade before trying to get a score this high. You can maximize points by shooting UFOs and collecting crystals to increase your point multiplier. That, and lasting for a long time. See All the Medals for tips on maximizing points.