Season the beef with salt and pepper and form into little balls about 1-1/2 to 2 inches in diameter.
Bring a pot of water to a boil. Add the onions. Drop in the meatballs and bring the water to a boil again. Cover, reduce the heat, and cook for 10 minutes.
Add the carrots and potatoes and cook until they are tender.
Remove some of the liquid and set aside. Drain, add peas if desired, and serve in large bowls. Pour a spoonful or so of the reserved liquid over each dish. Good accompaniments for Mish Mosh are rye bread and sour pickles.