How can I straighten a bunch of vertices into a straight line? (Odd angle) As you can see on the Top Ortho view, the selected vertices are a bit of a mess, and I need them to be perfectly aligned like the green line I draw next to them, while keeping the same, circle-ish shape.

How can I go about it?

I tried a few methods posted on this site and elesewhere but I never managed to make it the way I want it.

I would also prefer avoiding redoing the complete thing over again.

Thanks
This might work for you. Enable LoopTools in preferences then select the faces concerned rather than the vertices. Press W, choose "LoopTools", choose "Flatten".