Coat inside of pie pan with cooking spray. Cut roasted red peppers into 1/4" dice. Place a large pan over medium heat and add 1 tsp. olive oil to hot pan. Add spinach and roasted red peppers. Cook, stirring often, until wilted, 2-3 minutes. Remove from burner and season with a pinch of salt and pepper. Allow to cool, place in a wire-mesh strainer or kitchen towel, and squeeze out liquid. Measure out 1/2 cup flour and set aside. Place remaining flour in a mixing bowl with 2 Tbsp. olive oil, all but 2 Tbsp. yogurt, and a pinch of salt.

Mix dough until a loose, crumbly ball forms, 1-2 minutes Dough will be shaggy until kneaded. Lightly dust a clean work surface with reserved flour. Turn dough onto dusted surface and knead 5 minutes, folding dough over on itself and pressing down with the heel of your hand. Dough should be slightly sticky. If it feels too wet, add some reserved flour. If it feels too dry and crumbly, add some reserved yogurt.

Using a rolling pin or wine bottle, roll dough into a 13” circle about 1/4" thick. Dust underneath dough with more flour as needed to prevent sticking. Carefully lift dough into pie pan and press against sides. Avoid stretching dough. Instead, lift excess dough from sides further down into pan. Trim overhanging dough.

Spread ricotta on dough. Top with 1/3 the mozzarella. Chicago deep dish pizzas are "upside-down" and have cheese on bottom and sauce on top. Place an even layer of filling on cheese and add remaining mozzarella. Top with pizza sauce and season with 1/2 tsp. salt and a pinch of pepper.

Place pizza pan on prepared baking sheet (to catch any drips) and bake until crust is golden brown, 35-40 minutes. Remove from oven and cool 5 minutes. Cooling allows pizza to better hold together, making it easier to remove from pan.

Carefully remove pizza from pan with a spatula. You may have to bend or cut the disposable pan with scissors. Garnish with grated Parmesan, oregano, and red pepper flakes (to taste).