Preheat the oven to 350°F (180°C). Line a rimmed baking sheet with parchment paper.

In a small bowl, whisk together the flaxseed and water and let it sit until it begins to gel and thicken, about 5 minutes.

In a large bowl, use a large silicone spatula to combine the oats, cranberries, chocolate chips, pumpkin seeds, chia seeds, cinnamon, and salt. Add the peanut butter, mashed banana, flaxseed mixture, vanilla, and maple syrup and stir it all together until the dough is well combined and sticky enough to hold together.

Scoop ¼ cup (60 ml) rounds of dough onto the rimmed baking sheet, spacing them 1 inch (2.5 cm) apart.

Bake until the cookies are golden brown around the edges, 15 to 18 minutes. Remove from the oven, then use the bottom of a heat-proof cup or mug to gently flatten each cookie. You want them chunky.

Allow the cookies to cool completely on the baking sheet before serving.

Store any leftover cookies in an airtight container at room temperature for up to 5 days or in the refrigerator for up to 10 days.