Bring a large pot of salted water to a boil.

Cook the spaghettini until al dente.

Drain, reserving 1/2 cup of the pasta cooking water.

Heat the olive oil in a large skillet over medium-high heat.

Add the sausage and break it up into small pieces.

Cook the sausage until browned, about 8 minutes.

Add the garlic and cook until lightly browned, about 1 minute.

Add the tomatoes and cook until their skins begin to split, about 2 minutes.

Add the spinach and cook until wilted, about 2 minutes.

Remove from the heat.

Gently pop the tomatoes to release their juices using the back of a spoon.

Add the spaghettini and the reserved pasta water to the skillet.

Toss over low heat until the pasta is coated, about 1 minute.

Season with salt and pepper and serve.