convex planar (pair of sunglasses)
 

hi

can anybody help me with making the glass in a pair of sunglasses please.
I have created the shape of the curve but planar option only works on a planar curve. I cant seem to find a solution in the bevel option. Do I need to begin with a single line curve or a circle curve?
How do I planar this with a smoothconvex plane?

thanks