Boil a large pot of salted water and cook the linguine according to package directions until al dente.
Reserve 1/2 cup of starchy pasta water before draining the noodles.
Season salmon cubes with salt and pepper.
Heat olive oil in a large skillet over medium-high heat.
Sear salmon cubes for 4 minutes per side until golden brown, then remove from pan and set aside.
Reduce skillet heat to low.
Add Boursin cheese and half of the reserved pasta water to the skillet.
Whisk until the cheese melts into a smooth, thick sauce.
Toss in baby spinach and cook for 1 minute until softened.
Return salmon to the pan and fold in the cooked linguine until evenly coated, adding remaining pasta water if needed for consistency.