Rinse the Swiss chard leaves under cool water and trim the stems. Blanch them in boiling water for about 2 minutes until they soften, then plunge them into ice water to retain their vibrant color.

In a medium saucepan, combine rice and water, bringing it to a gentle boil. Reduce heat, cover, and simmer for about 15-20 minutes until fluffy and all water is absorbed.

Heat olive oil in a skillet over medium heat. Add chopped onions and minced garlic, cooking until translucent and fragrant, around 5 minutes.

In a large bowl, combine cooked rice, sautéed onions, ground beef, salt, pepper, and herbs. Mix until well incorporated.

Lay a blanched chard leaf on a flat surface. Place a generous spoonful of the filling near the stem end and fold in the sides before rolling tightly from the stem end.

In a saucepan, mix diced tomatoes with some salt and pepper; simmer for about 10 minutes until thickened slightly.

Preheat your oven to 350°F (175°C). Spread a layer of sauce in a baking dish, arrange the rolls seam-side down, then top with remaining sauce. Cover with foil and bake for 30-35 minutes.