Make the pizza sauce first. Finely dice the onion. In a pan over medium heat, add 2 tablespoons of olive oil and saute 1/4 cup of onion. When the onion has softened, crush in the garlic and stir.
Tip in 3/4 can of the canned tomatoes into the onion mixture. Add in the sea salt, 1 teaspoon dried oregano, paprika, chili flakes, and a good grind of black pepper. Stir and let simmer on low for 10 minutes or until the sauce has reduced and thickened. Taste and adjust to your liking, if you like it spicier feel free to add more chilis. Transfer the sauce to a bowl.
Preheat the oven to 350°F/180°C. Add the remaining 2 tablespoons of olive oil and 1/4 onion to a skillet pan and saute over medium-high heat until softened. Add the ground beef and saute until browned all over. Pour the pizza sauce over the beef mixture and stir through. Turn the stove off. Transfer the beef mixture to an ovenproof casserole if you are not using a skillet pan.
Layer 3/4 cup of mozzarella over the beef. Slice the red bell pepper and layer 6 segments over the cheese (easy for portions). Drop in the olives and capers and any other toppings of choice.
Sprinkle the remaining 3/4 cup mozzarella cheese over the peppers and olives. Then sprinkle 1/4 teaspoon dried oregano over the top to finish.
Bake in the center of the oven for 20 minutes or until the cheese has melted and turned golden. Serve immediately to enjoy the melted cheese.