Not really a "sandwich bar" (if there is such a thing in the U.S.), a place that I like and have eaten at recently (so I know it's still good) is The Grove at 690 Mission St. near Third St. It's one of a small local chain of two (formerly four, I believe, but the others were done in by the pandemic). You order at the counter, then sit at a table and your food is brought to you.

The Grove SF - Thoughtfully Crafted Comfort Food