Soak the sunflower seeds in water with a pinch of salt, for at least 4 hours, up to 12. Drain and rinse. Set aside.
Place 3 cups / 255g of the coconut in a food processor and blend on high until you have coconut butter (this can take up to 10 minutes, so be patient). Add the remaining ½ cup / 40 of coconut, the pulp, sunflower seeds, lemon zest, salt and maple syrup. Pulse to combine everything. Taste and adjust seasoning to suit your taste. The consistency should be light like cake crumbs, but will hold together well when pressed.
Transfer mixture to a lined 8x8” brownie pan. Press on the mixture very firmly, especially around the edges. Slice into 16 even squares, then place in the freezer for at least 4 hours.
To enjoy, remove the squares from the brownie pan, and break into separate pieces. Enjoy immediately. Store leftovers in the fridge or freezer.