Mondal's 135-run knock was the highlight of a fine batting performance by Bengal during which Sudip Chatterjee (51), Agniv Pan (70) and skipper Manoj Tiwary (45) also made noteworthy contributions.
At stumps, Pankaj Shaw (11) and Pragyan Ojha (2) were holding fort for Bengal after the side was put in to bat by Punjab.
On a rather frustrating day for Punjab, Sandeep Sharma and Vinay Chaudhary picked up two wickets apiece.
Mondal's knock was laced with 22 hits to the fence and came off exactly 200 balls.
Brief Scores:
Bengal: 332/5 in 89 overs (Sayan Mondal 135, Agniv Pan 70, Sandeep Sharma 2/70).