Shri Ganapati Atharvashirsha was written by Atharva Rishi who had Ganpati Darshan. 

Om Namste Ganpataye

Tvameva Pratyaksham Tatvamasi

Tvamev Kevalam Kartasi

Tvamev Kevalam Dhartasi

Tvamev Kevlam Hartasi

Tvamev Sarvam Khalvidam Bramhasi

Tvam Sakshadatmasi Nityam || 1 ||

O Lord Ganesha 

I Pay my deep homage to you, the Lord of the Deva-Gana 

You are the first facet of the Bramha-Tatva to arise 

You have alone created this Entire universe

You alone can maintain this universe 

You are indeed the all conquering supreme Lord 

Indeed you are the "ATMA" || 1 ||

Ganpati

Rritam Vachmi

Satyam Vachmi || 2 ||

Speak noble fact

Speak complete Truth || 2 ||

Ava tvam Mam

Ava Vaktaram

Ava Shrotaram

Ava Dataram

Ava Dhataram

Avanuchanamv Shishyam

Ava Paschatat

Ava Purastat

Avo Uttaratat

Ava Dakshinatat

Ava chordhvatat

Ava Dharatat

Sarvatomam Pahi Pahi Samantat || 3 ||

Protect me 

Protect the one who Describes you 

Protect all who hear about your characteristics

Protect me & the disciples who are under Tutelage 

Protect me from the obstacles (which arise during Rituals)

From the east (Similarly)

Protect me from the West,

From the North

From the South

Protect me from above & below

Protect me from all directions || 3 ||

Tvam Vangmayastvam Chinmaya

Tvam Anandmayastvam Bramhamaya

Tvam Sachitananda Dvitiyosi

Tvam Pratyaksham Bramhasi

Tvam Jnanmayo Vijnanamayo Asi || 4 ||

You are the constituent of speech

You are Joy & Immortal Consciousness

You are Truth, Mind & Bliss... one without a second

You are none other than divinity

You are Knowledge of Gross & Subtle types || 4 || 

Sarvam Jagadidam Tatvo Jayate

Sarvam Jagadidam Tvat Sti Shastati

Sarvam Jagadidam Tvay Layamesyati

Sarvam Jagadidam Tvayi Pratyeti

Tvam Bhumi Rapo Nalo Nilo Nabha

Tvam Chatvarim Vak Padaini || 5 ||

All the Universes manifest due to you 

All the Universes are sustained by you 

All the Universes get destroyed in you 

All the Universes finally get merged in you

You alone are Earth. Water, Fire, Air & Either 

You are the 4 types of speech & the root source of sound || 5 ||

Tvam Guna Traya Atitaha

Tvam Deha Treya Atitaha

Tvam Kala Treya Atitaha

Tvam Avastreya Atitaha

Tvam Muladhar Stiti Yosi Nityam 

Tvam Shakti Treya Atmakaha

Tvam Yogino Dhayayanti Nityam 

Tvam Bramhastvan, Vishnustvam, Rudrastvam, Indrastvam Agnistvam, Vayustvam, Suryastvam, Chndramastvam, Bramha Bhur Bhuva Svorom || 6 || 

You are beyond the 3 'GUNAS', (Satva; Pure, Rajas: Activating & Tamas: Dull) 

You are beyond the 3 Bodies; (Gross, Subtle & Casual) 

You are beyond Past, Present & Future (3 State of Time) 

You are beyond 3 states of being; (Awake, dream & Deep Sleep) 

You always Reside in the "MULADHARA" Chakra 

You are the trinity of Power; (Creative Maintaining & Destructive Powers) 

Sages always Meditate on you 

You are the creator. Sustainer, Destroyer, The Lord of 3 worlds, Fire, Air, Sun, Moon, You are all inclusive & all Pervading || 6 ||