How to fill gap between oven and vertical steel plate?

I am using a soft steel vertical plate as a front to the pizza oven. There is a gap between the plate and the stucco of the oven that I will fill with leftover insulating blanket and/or mortar or stucco in order to prevent and redirect any smoke exiting the front of the oven from rising between the plate and the front of the oven. Any suggestions as to what to use to fill that gap and seal between the steel plate and the oven stucco? Thanks.

I’d use the leftover insulation blanket as you first suggested. Seal with silicone high temp stove sealant to keep water out. I’d want to have a thermal break between the inner oven and the door plate as much as possible.

That’s what I’ll do. Thanks!