The 26-year-old first joined the Saddlers on loan from Chelsea in 2013. He then joined permanently in 2015 and was part of the team that narrowly missed out on winning promotion to the Championship.
Lalkovic spent last season in the Czech First League SK Sigma Olomouc.
But he has now been snapped up by Ostrava, who have ex-Villa striker Milan Baros among their ranks.
Ostrava missed out on a place in the Europa League on Saturday after losing a play-off clash with Mladá Boleslav.
And Lalkovic is hoping to play a key role in guiding the team back to continental competition.
“Looking forward to this challenge and fight for Europe,” he said. “Baník is a big brand and I’m grateful for the opportunity they have given me.”