Soak the pecans and cashews in boiling water for at least 15 minutes to soften (you can also do this overnight and don't need boiling water). Drain the water.
Preheat the oven to 350 degrees. Lightly grease a 9x9 baking dish or a 12 inch cast iron skillet.
In a food processor or blender, blend the bananas, both nuts, coconut, and chia seeds. Pulse until mixture is coarse (not smooth and overly mushy).
In a separate bowl, whisk together eggs, coconut milk, maple syrup, cinnamon and salt. Using a rubber spatula, remove the nut/banana mixture and add to the wet ingredients. Whisk until well combined. Now add in the baking soda.
Pour mixture in prepared pan. Top with additional sliced banana (if using), and diced pecans (if using). Transfer to the oven.
Bake for 30 minutes if using a large cast iron skillet. Bake for 40 minutes if using a square baking dish. Bake time will dependent on the size of the pan. At the 30 minute mark you can check the dish to see if the center is firm. Recipe will be toasty brown when ready. Remove from oven.
Let cool for at least 10 minutes before slicing and serving. Top with additional cinnamon or maple syrup (optional).