Meat
Start by removing the core of the onions - cut the tops and remove the core of each onion. Once that's done, set aside.
Get the onion core and chop into smaller bits.
Into a skillet over medium-low heat, add a drizzle of olive oil and the onions we’ve chopped, cook until slightly golden brown.
Add the crushed garlic cloves and mix until golden brown, add the green and yellow peppers, stir for another 2 minutes.
To season, add salt, black pepper and chimichurri, mix very well.
Chop the cherry tomatoes into round slices and add them to the skillet. Also add the ground beef, season it with salt, black pepper and chimichurri, mix and let it all cook for 10 minutes over medium heat.
Transfer the meat to a bowl and let it cool down a bit.
After doing this, add only the egg whites to the meat and mix well until combined.
After that, stuff the onions that we’ve hollow out with the meat.
On top of each stuffed onion, place an egg yolk.
Transfer the onions to a baking dish and bake in a preheated oven at 180°C (356°F) for 40 minutes.
After this indicated time, spread the mozzarella cheese over the onions and take them back to the oven for another 10 minutes or until the cheese melts.
Serve.