I got this recipe from a website called recipezaar.

Lemon Oatmeal Crumble

Cream:
2/3 C. butter (and really, use butter!)
1 C. brown sugar

Mix in :
1 C. Flour
1 t. baking powder
1/4 t. salt
1 C. rolled oats

Mixture should be crumbly.
Press half of the mixture into a greased 9" sq. pan.

Combine:
1 lemon zest
2 lemons juice
1 can sweetened condensed milk
Stir well.

Pour over crust.
Sprinkle remaining crust mixture over the top.
Bake at 350 degrees for 30 minutes.

The recipe said chill before serving, but being the gluttons we are, we had to sample it hot. Yummy! It's almost like a cobbler.
I would try it cold, or warm with a scoop of ice cream.
Recipe freezes well.

It was very easy to make.
I used one large Eureka lemon for the zest and juice, and added the juice from 3 small Meyer Lemons.

Now that sounds really good! I will try it & hopefully I will use some of my own lemons if they will ever grow again.