Combine 1 cup creamy peanut butter and ½ cup honey in a medium heat-safe mixing bowl. Microwave in 30-second intervals, stirring between each interval, until bubbles begin to form. Note: If your peanut butter is unsalted, stir in ½ teaspoon kosher salt.
Add 3 cups rolled oats to the peanut butter and honey mixture. Using a wooden spoon, spatula, or handheld mixer on low speed, mix until evenly incorporated.
Transfer the mixture to the prepared baking dish and use an additional piece of parchment paper to press the oat mixture into an even layer in the prepared pan. Chill the bars for 30 minutes in the refrigerator.
After chilling, remove the bars from the baking dish. Cut the bars into 12 squares. Enjoy immediately, or transfer to an airtight container, separating layers with parchment paper if needed, and refrigerate up to 5 days.
Notes
Peanut Butter: Shelf-stable creamy peanut butter is best, as it is thicker than all-natural peanut butter that needs to be refrigerated after opening. Oats: Old-fashioned rolled oats give the bars the best chewy texture, but quick oats can be used. The bars will just have a softer texture. Be sure your oats are certified gluten-free if needed. Vegan-Friendly: Replace the honey with pure maple syrup. The mixture will be softer and less sticky, so press it firmly into the pan and keep the bars refrigerated to help prevent crumbling.