Chop the onion and brown it in an oiled pan with half the parsley. Sprinkle with paprika.
Mix the meat with the cooked onion and the egg yolk.
Shape meatballs and cook in hot oil for about 10 minutes.
Prepare the sauce: melt the other 2 chopped onions in the oil with the thyme, salt and pepper. Add the tomatoes and simmer for 15 minutes.
Slice the pepper into strips and cut the zucchini into cubes. Cook for 5 minutes in boiling water, drain and pour in the sauce. Add the meatballs and continue cooking for 5 minutes.
Sprinkle with chopped parsley.