In a medium saucepan, heat about 2 inches of water to a simmer over medium heat. Place a steamer basket in the saucepan, add cauliflower florets, then cover and steam until very tender, about 15 minutes.
Place steamed cauliflower florets in the bowl of a food processor with 2 tablespoons of olive oil and process until smooth. Season with salt and pepper to taste, set aside. If the puree is to thick, add a bit of the steaming water and process to slightly thinner, spreadable consistency.
In a large oven proof skillet, heat 2 tablespoons of olive oil over medium heat. Add chopped leeks and diced celery and saute until softened, about 7 minutes. Add quinoa flour and stir to coat vegetables. Add water, stirring constantly until you have a smooth sauce. Bring sauce to a boil, reduce heat to medium low and simmer until thickened, about 2 to 3 minutes. Stir in lemon zest, fresh thyme leaves and fresh minced parsley. Season with salt and pepper to taste.
Add salmon pieces to the skillet and drizzle over with the fresh lemon juice. Finally add the fresh spinach leaves and gently toss everything to mix.