The violent images of war he witnessed have changed his life forever.
“The hardest part is the human side that you can’t train for,” Shannon, now 42, told SBS's Small Business Secrets.
“These places had been burned to the ground. There was nothing left in a lot of these villages."
"When we left in October  the mission was still in the balance, the kids were crying and coming on to the base and bawling in tears, and it was really hard to leave, you felt like you were deserting them.”
SBS LIFE: Learning Tetum, the language of Timor-Leste
Shannon struggled to return to his normal life. He said he constantly questioned the behaviour and motives of people around him, had trouble sleeping and withdrew from social activities.
He was diagnosed with hyper-vigilance, one of several symptoms that make up post-traumatic stress disorder (PTSD).
Professor David Forbes of Phoenix Australia, the national centre for post-traumatic mental health, says acquiring PTSD in a peacekeeping mission is just as likely for those who have served in combat situations.
“The rates of PTSD in peacekeepers is 17 per cent, so I think when we think about peacekeeping, we miss the fact that there is a lot of traumatic exposure.”
So Shannon set out to heal himself through philanthropy.
In 2012, Shannon and three other former soldiers had the idea to help people in Timor-Leste harvest wild grown coffee, originally planted by the Portuguese some 200 years ago. Locals receive a fair price for their exports.
“They just called us crazy foreigners. They were probably right!”
He set up Wild Timor Coffee Co. in Coburg, north of Melbourne.
Through the café, Shannon has raised more than $100,000 for water projects, schools and even a birthing centre in Timor-Leste.
But the business of coffee production is seasonal and has its limitations. So last year he and business partner Steven Dean, a former Australian Navy clearance diver, sought to expand his business ventures to a product that grows wild all year round; coconuts.
They built a factory in Lospalos, about 250 kilometres east of the capital Dili, employing women to produce coconut oil and providing a wage to anyone willing to collect coconuts.
The business is supporting around 50 families, but Shannon wanted to do more. So he now helps his biggest competitor in Timor-Leste to export her products to Australia.
Mana Dortia Kese runs a coconut oil business called HAFOTI in seven districts across Timor-Leste, and is grateful for the support from a man she calls ‘Maun Shannon’ or big brother Shannon.
"He said 'Mana we need to send coconut oil to Australia', and I say 'oh this is good news'."
She plans to expand and hire more women.
“After they have income we monitor them and we see their house improve, their children going to school, they getting access to health.”
The Wild Timor café is a hub for humanitarian activities, holding fund-raising events and donating money to disadvantaged people.
Barista Lauren Harrison said small donations make a big difference to people living in poverty.
“That’s one of the best perks about working here. It’s just awesome to know we’re putting our money and the good we’re doing is going to benefit someone else.”
And for Shannon, giving back is helping to overcome his own demons.
“When I walked around Timor, or when the army or Timor was mentioned, I was always going to have those visions, but now I have a positive mindset,” he said.