Place cubed focaccia in a large mixing bowl and drizzle with olive oil, dried herbs, and salt. Toss and stir to combine until all the pieces are somewhat evenly coated.
Arrange the cubed focaccia in an even layer on a shallow, rimmed sheet pan. Give them a bit of breathing room so they're not all pressed up against each other.
Place the sheet pan in the oven and leave the croutons to dry. Stir or shake the pan every 15-20 minutes to help them dry evenly. This can take anywhere from 45 minutes to 2 hours, depending on the moisture content of the bread, how dry it was to start with, and how much oil it absorbed.
To test a crouton for doneness, remove one from the pan and let it cool slightly. Bite into it. When the center is completely dry and crispy, your focaccia croutons are done.
Let croutons cool completely before storing. Store in an airtight container for 2-3 weeks.
RECIPE NOTES
If using other seasonings, aim for about 2-2½ teaspoons total. Different seasoning blends have different intensities, adjust accordingly!
Once your focaccia croutons are fully dried out and cooled, store them in an airtight container; you may find tucking a paper towel inside helps absorb any excess moisture. Focaccia croutons can be stored in an airtight container at room temperature for two to three weeks. You can also refrigerate them or freeze them for up to 3 months. If your croutons seem to be a bit soggy after a day or two in storage, they probably weren't fully dry when you took them out of the oven or the container wasn't fully sealed. Crisp them back up in the oven at 350°F for a few minutes before using them.