Preheat oven to 375°F. In a medium skillet over medium heat, sauté the onion and bell pepper in the olive oil until softened, about 5 minutes. Add the garlic and cook for another minute. Stir in the oregano and basil, season with salt and pepper to taste.
In a small bowl, whisk together the tomato paste and water until blended. Spread over each naan flatbread.
Top each pizza with the sautéed vegetables and sprinkle with mozzarella cheese.
Bake for 15 minutes or until cheese is melted and bubbly.