According to ganesh shastras, it is given that his "mantra japa" should be done while eating fruits or laddu (a round shaped sweet).
To get siddhi or fruit, one should recite his mantra for 16,000 times.Below is the Tantrik Ganesh mantra:
Asyashree Tantrik ganesh mantrasya Sughora rishihi nibhida gayathree Chandhaha Tantrik Ganapathirdhevata mama sarvabheesta sidhyarthe jape viniyogaha
Om Sughora rishaye namaha shirasi
Om nibhida gayathree chandhase namaha mukhe
Om Tantrik ganapathaye namaha hrudhaye
Viniyogaya namaha Sarvange
Om Heering angustabhyam namaha
Om ganga tharjaneebhyam swaha
Om hasti madhyamabhyam vashat
Om peesachi anamikabhyam hoom
Om likhe seaha karathalakara prastabhyam phat
Om heering hrudhayaya namaha
Om ganga shirase swaha
Om hasti shikhayai vashat
Om peesachi kavachaya hum
Om likhe nethrathrayaya vaushat
Om swaha asthraya phat
Rakthamoorthim ganeshancha sarvabharana bhooshithamRakthavasthram threenethram cha rakthapadmasane sthithamChaturbhujam mahakayam dhvidantam susmithananamIstancha dakshinehasthe dantham cha dhadhathaha karePashankushou cha hasthabhyam jatamandala vestithamLalate chandrarekhadyam sarvalankara bhooshitam
Then start jaap Tantrik Ganpati Mantra
"Om heering ganga hasti peesachi likhe swaha"
Jaap:--- 500000 within 21 days