I’m probably giving away super-secret info (my first job was at a Bruegger’s and I worked there for nearly 3 years), but here’s what we did in that store:
We used 2-day old bagels (leftover bagels were packed up at the end of the night and bagged for the next day as “day old” bagels. At the end of the next day, those are what we’d make bagel chips).
-Step 1: Slice them into slices maybe 1/8" thick.
-Step 2: heat your oven to 425 (I think that’s the temp our oven was at–we used the same temp that we baked at)
-Step 3: spread the slices on a parchment-covered baking sheet so that they’re one layer thick
-Step 4: cook until golden brown (sorry for no time, it was over 5 years ago). You may want to flip them over once while cooking to brown both sides.
No seasoning needed. Usually I’d cut up a couple salt (or everything bagels, which have salt) bagels for the flavor.