Whisk the spelt flour, sugar, baking powder, salt, orange zest, and poppy seeds together in a large bowl.
Add the canola oil, blood orange juice, and water and mix until blended.
Pour the batter into the prepared pan. Lay the blood orange slices on top of the batter.
Bake at 375 degrees for about 30-35 minutes until the edges are lightly golden brown, and a toothpick inserted in the middle comes out clean.
Cool completely before serving.
Notes
Store leftover cake in the refrigerator in an airtight container. It should stay fresh for up to 4 days.If you can't have poppy seeds, go ahead and leave them out.I have not made this recipe with gluten free flour, so I'm not sure how well it will work.