Heat large sauté pan over medium with 1 tbs olive oil.
Sauté onion until softened. Add mashed potatoes and cook until they warm and loosen. Add spinach and stir until wilted.
Transfer mixture to a mixing bowl, and stir in eggs, flour, and baking powder.
Wipe clean the sauté pan and heat 2 tbs olive oil over medium-high heat.
Working in small batches, drop in rough tablespoons of the mashed potato mixture, cooking each side for 2 minutes or until golden. You may need to add more olive oil as you go.
Serve immediately, while still warm. Sprinkled with salt and pepper to taste, as well as freshly grated Parmesan if desired.