"We have put what happened behind us, emotionally we are stable and we are fully focused on the game," Tuchel told reporters at a press conference at the Stade Louis II on Tuesday.
Last week's first leg was postponed by 24 hours after a bomb attack on the Dortmund team bus en route to the game in Germany.
A policeman was injured along with Dortmund's Spanish international defender Marc Bartra, who needed surgery on a broken wrist after being hit by flying glass.
Three separate claims of responsiblity have been made for the attack but police are still looking for suspects after an Iraqi man was arrested and later cleared of involvement.
When the game finally went ahead at Signal Iduna Park Dortmund lost 3-2 and Tuchel later fumed at UEFA for allowing the match to be played at all.
But as they try to turn the tie around in the Mediterranean principality, he added: "What happened last week has brought us together and made us even stronger.
"Now we need to put in a good performance and I am convinced we can do it."
Dortmund's chances of reaching the semi-finals are boosted by the presence of German international star Marco Reus.
He was injured for the first leg so was not on the bus that was attacked, but he returned to score in the 3-1 home win over Eintracht Frankfurt in the Bundesliga at the weekend.
"I was at the stadium when I learnt the news," Reus, 27, said of the attack.
"Each player has his own way of dealing with what happened. I have a certain age and some experience, so my goal is to help the players, see if I can talk to them, support them.
"This has brought us closer together. We are a real team, a real group and we want to demonstrate that tomorrow (Wednesday)."