Well for me here would be what I would do.
I would alternate between these:
Warm up 15 minutes then spend 30 minutes in hr zone 3.
Spin in a gear that allows you a cadence of 50 - 60 rpm then every 3 - 5 minutes stand up then while in the saddle drive the pedals down as hard as possible for 15-20 revolutions of the cranks.
Spin ups. Slowly spin-up to max rpm over 30 seconds. When you begin to bounce, back off and then hold it for several seconds. Do this several times.
Tempo intervals. After warm up do 4-5 x 6 minutes in the 3 zone (2 minute recoveries).
One leg spins. Do 30 seconds to 60 seconds a time with isolated leg training. You can also do this by just favoring one leg as much as possible for a minute or two then switch to the other leg.
Just some ideas, if you do some of them you should notice some nice results later on. Make sure that every two or three days you have a rest day, either off the bike or just an easy ride.
I may be fat but I'm slow enough to make up for it.