A very simple one but sometimes simple is best.
half a can tuna flakes, drained
some passata (mine was from last year's tomatoes)
half a small onion, peeled and thinly sliced
a bit of oil (or butter)
a mushroom, sliced
herbs and seasonings
Cook the spaghetti
While that is cooking, saute the onion in the oil until it softens and goes translucent. Add the mushroom and cook a little bit longer. Add the passata with herbs, salt and pepper and simmer for a short while until; it reduces a bit. Taste and adjust seasonings if needed.
Add the tuna flakes and stir gently.
Tip in the cooked, drained spaghetti, gently mix and serve.
(If you want, before serving, top with some grated cheese and bake under the grill for a short while so the cheese melts. I didn't)