Cook pasta in salted water for 10-12 minutes al dente, adding frozen peas for the last 2 minutes. Drain, allow to drain.
Peel onions, cut into cubes, set aside a few onion cubes and peas.
Dice tomatoes, mix pasta with peas, tomatoes and onions in a bowl.
For the mayonnaise, mix egg yolks with salt, mustard, pepper and juice of one lemon.
Add oil first drop by drop, then in a thin stream.
Drain tuna, add to mayonnaise and blend together.
Stir whipped cream and milk into sauce.
Mix the sauce into the pasta, garnish with diced onion and peas.