Katherine, congrats on the nearly 13 years--me too!
I started eating oats every day for breakfast in mid-May 2010. I realized I didn't want it to boil over in the microwave, so I make my 1/2 oats (with either 1 or 1 1/2 cups water) in a 4-cup (~1-liter) Pyrex bowl. I never boils over (unless I hit too many zeroes on the microwave
)
When I use the 1 1/2 cups water, I cook for 8 minutes at 50% power, and it won't boil over. I've gone so far with this that when I used to travel, I'd bring the 4-cup Pyrex bowl with me. My husband hates my luggage sometimes.