Preheat the oven to 350°F (175°C). Grease an 8x8-inch baking dish with coconut oil.
In a large bowl, whisk together the whole spelt flour, sweet rice flour, baking soda, cinnamon, cardamom, and sea salt until evenly combined.
In a separate bowl, combine the ground flaxseed with 1/4 cup water and let sit for at least 5 minutes to thicken, then add the mashed bananas, sugar, instant espresso, vanilla, melted coconut oil, and non-dairy milk; mix until smooth.
Pour the wet ingredients into the dry ingredients and stir gently until just combined; avoid overmixing.
Fold in the dark chocolate chips, then transfer the batter to the prepared baking dish and spread evenly.
Bake for 40 minutes, or until a toothpick inserted near the center comes out mostly clean with a few moist crumbs.
Allow the cake to cool in the pan for at least 15 minutes before slicing; it tastes best when fully cooled.