Zest the orange carefully to keep it from deforming it. You just need the orange colored part.
1 large orange
With a sharp knife, slice the orange into thin and uniform slices.
Using paper towels, dry the orange slices by pressing them in between folded sheets of paper towel.
Arrange the dried orange slices inside the pan, with a bit of overlap, and set aside.
For the cake
Whisk together almond flour, oat fiber, psyllium husks baking powder, baking soda and salt. Alternatively, you can later sieve them directly over the wet mixture.
1 1/2 cup (154 g) almond flour, 1/2 cup (50 g) oat fiber, 1 tablespoon whole psyllium husks, 2 teaspoons baking powder, 1/8 teaspoon baking soda, 1/4 teaspoon salt
In a separate, larger bowl, whisk together the olive oil and sweetener.
1/2 cup (110 g) olive oil (light taste), 3/4 cup (130 g) granulated sweetener
Add the eggs, one by one, whisking after each addition. Continue mixing for 3 more minutes, until the batter is pale and foamy.
3 eggs
Add the yogurt, orange extract and orange peel, and whisk it for a minute more.
Drop (or sieve in) the dry mix onto the wet mix, and combine it all very well with a spatula until homogenized. The batter will look very shiny and thick.
Take the prepared pan, and if necessary dry up the orange slices arrangement with a paper towel before pouring in the batter.
Bake on the middle rack position in the preheated oven at 350 °F (175 °C) for the first 25 minutes. Then loosely cover the top with an aluminum foil and turn the oven temperature down to 320 °F (160 °C), and bake for another 35 minutes.
Remove the foil to test for doneness. The cake is ready when it's pulling from the edges and the top is just firm to the touch.
Notes
I used an 8 -inch hemisphere pan. You can use any 8 -inch pan, or a tall 7 -inch pan, or a medium loaf pan.Using room temperature or slightly warm butter or ghee (instead of just out of the fridge) makes it easier to spread a thicker buttering layer. You'll need a thick layer under the orange slices.The cake must be turned while it’s still warm, to prevent the orange slices from sticking to the bottom it cools.If gluten-free, make sure the oat fiber is gluten-free certified. Although oats are naturally gluten-free, there may be cross-contamination from wheat crops or during processing, as some brands state in their packages.Nutrition information shows recipe made with oat fiber. Recalculate for pea protein substitution.