Preheat the oven to 350 degrees F (175 degrees C). Line a large cookie sheet with parchment paper.

Gently mix oats, dates, hazelnuts, almonds, raisins, cranberries, pretzels, and chia seeds in a large bowl.

Mix water and flax seeds together in a small bowl. Let stand until thickened, about 5 minutes.

Mix pumpkin puree, bananas, and honey together in a medium bowl. Gently mix into the oat mixture until soft and evenly combined. Spread onto the cookie sheet in an even 1/2-inch layer.

Bake in the preheated oven until browned but still slightly gooey, 25 to 33 minutes. Let cool before cutting into bars.