In a large bowl, crack the egg, add the salt, and whisk lightly with a whisk or fork.
Pour in the rice flour and mix well.
Add the cornmeal to the bowl and mix again until combined.
Add the baking powder and stir again.
Gradually pour in the kefir, mixing until the batter is smooth.
The batter should be completely smooth, with no lumps.
Add the ground flaxseed and mix to incorporate.
Add the whole flax seeds and sunflower seeds.
Pour in the oil and mix everything well. The batter should have a medium consistency, not too runny but not too thick.
Carefully pour the prepared batter into a silicone loaf pan.
Sprinkle the top with sunflower seeds or sesame seeds, if you like, and score the top lengthwise with a knife.
Place the pan in the oven and bake at 350°F (175°C) for 30–35 minutes.
Let the baked loaf cool completely, then slice and serve with your favorite dishes.