Januzaj made just nine Premier League starts across two seasons under Van Gaal and endured a less than successful loan spell at Borussia Dortmund during the 2015-2016 campaign.
Van Gaal's successor Jose Mourinho also deemed Januzaj surplus to requirements and loaned him to Sunderland for the previous season, before the Belgium international decided a permanent move away from Old Trafford was best for his career, agreeing a five-year deal at Sociedad last month for a reported fee of $A16.4 million.
Currently struggling with a hamstring injury, Januzaj sat out Sociedad's 3-2 win at Celta Vigo last weekend to open its LaLiga season, and the 22-year-old has special plans for Van Gaal when he opens his account.
"If I score a goal I will dedicate it to Van Gaal," Januzaj said.
"I don't want to talk about him, but everyone knows how many problems I had with him.
"We didn't have the best of rapports. It wasn't easy, it's very frustrating and difficult when you are in a situation like that."
Although Mourinho also sent him out on loan, Januzaj bears no ill-feeling towards the Portuguese.
"I have nothing bad to say about Mourinho," he said. "I have no criticism of him as a coach. From the beginning he was fair."