Coarsely crumble the toast bread. Heat butter in a pan. Roast the crumbs in it while constantly turning, take them out and let them cool down.
Cook spaghetti in 3-4 l boiling salted water (approx. 1 teaspoon salt per litre) according to package instructions.
In the meantime, cut the bacon into fine strips and fry until crispy in the pan. Peel onion, dice finely and add with the frozen peas. Fry for about 5 minutes.
Slice the parmesan into thin shavings and mix with the roasted breadcrumbs. Drain the spaghetti and fold into the pea vegetables. Season to taste with salt and pepper. Arrange spaghetti-peas-pan with cheese crumbs.