Heat oil in a medium size skillet, add onions and 1/2 tsp kosher salt, cook until onions are starting to soften. Add chorizo and oregano, cook until onions have lost most of their moisture and are starting to caramelize. Remove from heat and allow to cool to room temperature.
Preheat oven to 350℉.
In a small bowl whisk together flour, baking powder, 1/2 tsp salt, garlic powder and onion powder.
In a large bowl whisk together eggs and oil. Add sour cream and whisk until smooth. Add spinach and stir to combine.
Add dry ingredients to wet all at once. Whisk until combined, but do not over mix. Stir in onions, chorizo and cheddar cheese.
Spread evenly onto a parchment lined 15″x10″ baking sheet. Bake for 25-30 minutes until center is set.
Remove from oven and allow to cool for 5 minutes. Slide the entire cake onto a cutting board by loosening the edge, grabbing a corner of parchment and pulling the entire piece onto the board. Cut into 16 squares and serve immediately.
If using at a later time, pull out of the pan as above and allow to cool on a wire rack. When cool, cut into squares. Rewarm and crisp squares in toaster when ready to serve.
Wrap two squares together with plastic wrap and store in a sealed container or zip lock bag in the freezer. Will keep frozen for up to two months.