125 Special Attack > 95 Attack.
A good set would be:
Exeggutor (M) @ Sitrus Berry / Life Orb/ Choice Specs
252 Special Attack/ 200 HP/ 56 Defense
- Leaf Storm [Primary hard-hitting STAB] / Giga Drain
- Sludge Bomb
- HP [Fire]
Evs to let it live a U-turn (hopefully. STAB U-turns can still KO it, however). Speed is paltry, so don't try too much to increase it. Not really worth it.
Typical set, to be honest, but gets the job done. Psyshock for them Special Walls.
Edit: Forget the U-turn thing.
>252 Atk Choice Band Technician Scyther Bug Bite vs. 252 HP / 48 Def Exeggutor: 844-1000 (214.2 - 253.8%) -- guaranteed OHKO
Rest all is the same. Invest in Speed instead (not recommended, but can be done).