Several years ago there were many enthusiasts who tried to organize their curricula around essential questions. They created a few schools in New York City, called Essential Schools. I am not sure if those schools still follow the UbD principals, but you can try to Google them and contact their principals. I knew one of them he was a real fanatic of "meaningful education". In the beginning of the year the entire staff would get together and decide what "Essential Questions" they want the students to learn and those questions were repeated and learned in all classes in all subjects to create the real life connections in the heads of the students instead of teaching each subject separately. All projects were interdisciplinary. If you saw a movie "School of Rock", I think it was inspired by the UbD ideas.
When I had several PDs in this area the level of Math was always high elementary or middle school. Again you can Google projects in Math, whatever you find will be kind of UbD, because, I believe they are very similar with project based learning.
I can give you one very concrete example of such project: Planning House Repairs.
You tell the kids that you want to paint the classroom.
(you have to be prepared to really paint it at the end of the project :) because it is the most fun :)
What do you need? Paint
How much? Calculate
Measure the width, length and the height of the room.
Calculate the area of each wall, and celling.
Bring a can of paint to class read the information on the can how much surface will be covered with 1 can of paint.
Calculate how many cans do you need of each color.
Calculate how much money you have to collect to buy this paint.
The project if it is supported by your administration will be unforgettable, and nobody will need to review area topic.
Right opposite on this base you can easily teach an area of a triangle and all other figures.
Remember just one thing you are not talking, they are doing all of the project on their own, don't try to explain anything, just lead them away from mistakes and misunderstanding.
I know it is a very primitive and simple project.
A better one for a high school was a film production. It was a whole school project and they had directors, camera people, scenario writers etc. etc.
Another is Planning a Trip. This one will teach them speed, distance, time, places, easily related to geography, social studies and more.
For High Schools Math there is always a lack of good projects. You and me can create a few if you are a HS teacher. I do have ideas :)
Here is my email address: email@example.com