For the roasted red pepper harissa: Place the red peppers under a very hot broiler; broil, turning occasionally, until blackened on the outside and completely soft, about 20 minutes. Transfer to a bowl, cover with plastic wrap and allow to cool. Peel the peppers and discard the skin and seeds.
Heat the olive oil in a pan over medium heat. Add the onion, garlic and cumin and saute until golden brown.
Combine the roasted red peppers, the sauteed onion mixture and the lemon juice in a blender or food processor. Blend until smooth, adding a little more oil if needed. Season with salt.
For the cauliflower crust: Place a pizza stone in the oven and preheat to 450 degrees F. Let the pizza stone heat for at least 30 minutes.
Chop the cauliflower into small pieces and then pulse to fine grains (resembling couscous) in a food processor. Measure 2 cups of the pulsed cauliflower and place in the center of a clean side towel along with 1 teaspoon salt.
Wring the cauliflower of its liquid by twisting the side towel around the cauliflower and twisting with your hands to remove excess water.
Combine the mozzarella, Parmesan, eggs and pepper in a medium bowl. Grate the garlic clove into the bowl and then add the cauliflower. Mix together until thoroughly combined.
Spread the cornmeal in a circle on a half sheet of parchment.
Form the cauliflower mixture into a ball, place it on the cornmeal and evenly spread into a 1/4-inch-thick round. Pinch the edges of the crust to form a rim.
Using a pizza peel, transfer the parchment of cauliflower crust onto the preheated pizza stone. Bake for 15 minutes.
For the toppings: Saute the merguez over medium-high heat until cooked through and browned, about 10 minutes.
Toss the arugula in some olive oil and season with salt.
Once the pizza has cooked for 15 minutes, spread it with harissa to the edges. Then evenly top with the goat cheese, merguez and some sliced olives.
Return to the oven and bake for an additional 5 minutes. When the cheese is melted and starting to bubble and brown, slide the pizza peel under the parchment and remove the pizza to a pizza pan.
Let rest for a few minutes, then top with arugula and pecorino. Slice and serve.