Sift rice flour, tapioca flour, potato starch, yeast, xanthan gum, salt and baking powder together in a bowl.
Place quinoa, sunflower seeds, almonds and flaxseeds in a coffee grinder. Grind until very fine. Transfer to the rice flour mixture. Mix until new dry mixture is well combined.
Combine milk, eggs, egg whites, treacle, agave nectar, olive oil and vinegar in the bowl of a stand mixer fitted with the paddle attachment; beat on low until well blended. Pour in dry mixture slowly, beating on medium-high and pushing dough down with a spatula as necessary.
Scoop dough into the prepared pan, spreading it evenly with a wet spatula. Sprinkle with sesame seeds. Fill a large bowl with boiling-hot water and place it in a microwave. Rest a cooling rack on top of the bowl. Place pan on top and cover the dough. Let dough rise until it reaches the top of the loaf tin, about 1 hour 30 minutes.
Bake in the preheated oven until the top is golden and the loaf is cooked through, about 45 minutes. Let bread cool thoroughly before slicing with a serrated knife.