In a bowl, combine flour, sugar, yeast, and salt.
Add cold water and olive oil, then mix to form a dough.
Knead the dough for 5 to 7 minutes until smooth.
Cover and let the dough rise for 1 hour.
In a small bowl, mix tomato sauce, tomato paste, sugar, Italian seasoning, fennel seeds, and garlic powder to make the sauce.
Soak the sliced onions in cold water for 10 minutes, then drain and pat dry.
Break the Italian sausage into small pieces.
Preheat the oven to 475°F (245°C).
Divide dough if making two pizzas, then roll very thin on a floured surface.
Transfer dough to a baking sheet dusted with cornmeal.
Spread a thin layer of sauce over the dough.
Add shredded mozzarella cheese evenly.
Top with crumbled sausage and sliced onions.
Sprinkle dried oregano and optional crushed red pepper flakes.
Bake for 12 to 15 minutes until the crust is crispy and golden.
Slice into squares and serve hot.