Place the cauliflower on a rimmed baking sheet and toss with 2 Tbsp extra virgin olive oil, season with a few pinches of kosher salt and freshly ground black pepper. Place in preheated oven and roast 20 minutes until some of the cauliflower has golden spots. When done, remove pan from oven, set aside, and reduce oven temperature to 350 degrees F.
Heat 1 Tbsp olive oil in a large skillet over medium-high heat. Add the pancetta, onion and red bell pepper and cook 4 minutes. Add fresh spinach and minced garlic and cook 2 – 3 minutes more until lightly brown. Remove from heat, stir in parsley and roasted cauliflower, and set aside.
Spray a 9-inch ceramic or glass deep-dish pie plate or tart pan with cooking spray and sprinkle 2 Tbsp Parmesan in the bottom. Place on a baking sheet. Whisk together the half-and-half, eggs, egg yolks, and all-purpose flour in a pourable bowl. Season with salt and freshly ground black pepper to taste. Spread half of the cauliflower mixture evenly in the tart pan and top with half the feta cheese. Repeat steps with the other half of cauliflower mixture and cheese. Carefully pour the egg mixture over the ingredients in the tart pan. Sprinkle remaining Parmesan on top.
Bake at 350 degrees F until the quiche is just set in the center, about 45 – 50 minutes. Cool at least 10 minutes, then serve.