The prolific striker was absent for BVB's hard-fought 2-1 win at Werder Bremen last time out in the Bundesliga due to his AFCON duties with Gabon, with Andre Schurrle on target after taking his place up front.
Gabon's exit at the group stages means Aubameyang has returned to club duty, though, and Tuchel has seen enough in training to be convinced that the pacy forward is ready to face Mainz on Sunday.
"Aubameyang has taken part in two intense training sessions since his return," Tuchel stated at a news conference.
"He is ready to play again, so he will play."
Aubameyang's return coupled with the arrival of exciting Swedish teenager Alexander Isak means Tuchel has plenty of options in attack.
And the BVB boss is happy to have such a selection headache ahead of Dortmund's trip to his former club.
"It is a good thing for a coach when you have a lot of options," he added.
"I have a number of tough decisions to make. But we are not afraid to make such decisions."