Preheat the oven to 425°F. Place the pizza crusts on parchment-lined baking sheets.
In a small bowl, mix the olive oil, minced garlic, salt, and pepper.
Brush the garlicky olive oil mixture evenly over the top of the pizza crusts, using a pastry brush or silicone brush.
Assemble the pizza by evenly spreading the cooked sausage, fennel, and red peppers over the prepared crusts. Spread the mozzarella cheese evenly over the toppings.
Bake for 10-12 minutes until the cheese is melted and the crust is golden brown. Let pizzas cool for 5 minutes before cutting into slices to serve. While the pizza is cooling, sprinkle red pepper flakes and a few fresh fennel fronds on top for garnish.