Bring a large pot of water to a boil. Trim the ends of each onion and carefully peel away the outer layer. Simmer the onions for 10–15 minutes until softened. Let cool, then gently separate the layers. You’ll want at least 2–3 intact outer shells per onion to stuff.
In a large bowl, combine cooked rice, onions tomato paste, garlic, herbs, olive oil, salt, and pepper. Mix well until all ingredients are evenly distributed.
Lay out one onion shell at a time and spoon 1–2 tablespoons of filling into the center. Roll or fold closed. Repeat until all filling and onion layers are used.
Preheat oven to 375°F (190°C). Lightly grease a baking dish with olive oil. Arrange the stuffed onions seam-side down. Brush the tops with olive oil and season with salt and pepper. Cover with foil and bake for 25–30 minutes. Remove foil and bake another 10 minutes for a golden finish.
Let cool slightly before serving. Garnish with fresh herbs and an extra drizzle of olive oil if desired.