Preheat the oven, on the grill setting, at 400°F / 200°C.
Heat the olive oil in a large heavy-bottomed pot over medium-high heat.
Add the diced red onion, and sauté for about three minutes, until just translucent.
Add the crushed garlic, and sauté for about two minutes more.
Add the diced eggplant, zucchini, and red pepper, along with the oregano, paprika, salt, and pepper.
Sauté the vegetables for about 5 minutes, stirring frequently.
Add the diced tomatoes, and stir to combine with the vegetables.
Allow this mixture to simmer over medium heat for 15 minutes, stirring frequently.
Arrange the sliced halloumi in a single layer on top of the ratatouille.
Place the pot into the oven, and bake the halloumi under the grill for 5 minutes, until golden brown.
Remove from the oven, and serve hot!