Cook the arborio rice per the package instructions. Set aside and let cool down.
Adjust rack to middle position and preheat oven to 400 °F.
Meanwhile, warm up a drizzle of olive oil in a saute pan over medium high heat. Add in the chuck roast ground meat and saute for about three minutes until mostly browned. Lower the heat to medium and add in the onion. Cook for about two minutes, making sure to stir occasionally so that it cooks evenly.
Lower the heat to medium low and stir in the peas. Cook for about five minutes and then mix in one cup of the tomato sauce over low heat. Once mixed, remove the pan from heat and set aside to cool off.
Add one cup of the tomato sauce to the cooled off rice and mix until fully combined. Spread half a cup of tomato sauce evenly onto the bottom of a 10" x 10" baking dish. Add half of the rice into the baking dish and spread evenly over the tomato sauce.
Scoop the meat mixture on top of the rice in the baking dish and spread evenly. Add the pearl mozzarella over the meat layer and then top of with half of the pecorino cheese. Cover with the rest of the rice. Pack the rice down evenly and then place the baking dish into the oven for twenty minutes.
Remove the baking dish from the oven and cover with the remaining pecorino cheese and shredded mozzarella cheese. Place back into the oven for about another ten minutes or until the top layer of cheese has melted down.
Remove from the oven and let sit for about ten minutes. Cut into your desired serving sizes and enjoy. Salute and cin cin!