Preheat the oven to 375°F (190°C).
Cook the jumbo pasta shells in salted boiling water until al dente, about 10 minutes. Drain and set aside to cool slightly.
Heat olive oil in a medium skillet over medium heat. Add the chopped onion and sauté until soft and translucent, about 5 minutes.
Add minced garlic to the onions and cook for an additional 1 minute until fragrant. Remove from heat.
In a food processor or blender, combine the drained chickpeas, sautéed onion and garlic, ricotta cheese, parsley, Romano cheese, egg whites, ground nutmeg, and salt. Blend until smooth and well combined.
In a large saucepan, combine crushed tomatoes, water, dried basil, and 0.25 tsp salt. Bring to a simmer over medium heat, then reduce heat to low and cook gently for 10 minutes, stirring occasionally.
Spread about 1 cup of the tomato sauce evenly in the bottom of a 9x13-inch baking dish.
Stuff each cooked pasta shell with the chickpea and ricotta filling and arrange them in the baking dish on top of the sauce.
Pour the remaining tomato sauce over the stuffed shells, making sure they're well covered.
Sprinkle shredded mozzarella cheese evenly over the top.
Cover the dish with foil and bake for 25 minutes. Remove the foil and bake an additional 10-15 minutes until the cheese is melted and bubbly.
Let the stuffed shells rest for 5 minutes before serving. Garnish with extra parsley if desired.