In a pot, bring some salted water to the boil then cook the potatoes until tender.
Drain and set aside.
Heat 2 teaspoons of oil in a medium non-stick pan over medium heat.
Add the onion and cook, stirring, until translucent.
Add the potatoes, thyme and paprika and cook for 2 minutes more.
Lightly whisk eggs and egg whites in a large bowl.
Gently stir the potato mixture into the eggs along with cheese, spinach and some salt and pepper until combined.
Add the remaining 1 teaspoon of oil and heat on medium.
Pour in the egg mixture, cover and cook until the edges are set and the bottom is browned, 4 to 5 minutes.
Run a spatula gently around the edges to loosen them.
Invert a large plate over the pan and turn out the tortilla onto it.
Slide the tortilla back into the pan and cook until completely set in the middle, 3 to 5 minutes.
Serve warm or cold in sliced with a green salad if you like.