Set a large saucepan or Dutch oven on the stove over medium heat.

Pour the olive oil into the pot and let it warm for about 30 seconds.

Add the chopped onion and 1/2 teaspoon of the kosher salt to the pot.

Cook the onion for 5 to 6 minutes, stirring often, until it is soft and translucent. Lower the heat slightly if it starts to brown.

Pour the water into the pot and raise the heat to high.

Bring the water to a full boil.

Add the ditalini to the boiling water and stir well so the pasta does not stick to the bottom of the pot.

Cook the pasta for 3 minutes, stirring once or twice.

Add the frozen peas to the pot and stir them into the pasta.

Boil gently for 6 to 8 minutes, stirring often, until the pasta is tender and the liquid looks slightly thickened but still brothy.

While the pasta cooks, make sure the Parmesan is finely grated and the lemon is zested and cut into wedges.

Lower the heat to low when the pasta is tender.