Heat oil in the pressure cooker over medium heat and saut� onion and garlic until softened. Add tomato sauce, stock and carrots and bring to a boil. In a separate bowl, mix together beef, pork, rice, egg, salt and pepper. Form mixture into 1-inch balls. Drop meatballs into boiling stock mixture. Seal cooker, bring up to high pressure, reduce heat to stabilize pressure and cook for 10 minutes. Remove cooker from heat and release pressure. Taste and adjust seasonings. If desired, stir in peas and simmer for 1 to 2 minutes.