Before starting, wash and dry all produce. Add 10 cups water and 2 tsp salt to a large pot (use same for 4 ppl). Cover and bring to a boil over high heat. Add linguine to the boiling water. Cook uncovered, stirring occasionally, until tender, 10-12 min. Drain and return linguine to the same pot, off heat.

Meanwhile, peel, then finely chop shallot. Thinly slice mushrooms. Roughly chop spinach.

Heat a large non-stick pan over medium-high heat. When hot, add 1 tbsp (2 tbsp) butter, then swirl the pan until melted. Add shallots. Cook, stirring often, until softened, 2-3 min. Add mushrooms and 1/4 tsp (1/2 tsp) garlic salt. Cook, stirring occasionally, until mushrooms begin to soften, 2-3 min. Add soy sauce. Cook, stirring often, until mushrooms are tender, 2-3 min. Season with pepper.

Reduce heat to medium. Stir cream cheese into mushroom shallot mixture. Cook, stirring often, until cream cheese melts, 1-2 min. Add cream. Cook, stirring often, until sauce thickens slightly, 2-3 min. Add spinach. Stir until wilted, 1-2 min. Season with 1/4 tsp (1/2 tsp) garlic salt and pepper.

Pour mushroom Alfredo sauce into the pot with linguine, then toss to combine.

Divide mushroom Alfredo linguine between bowls. Sprinkle with Parmesan. Sprinkle chili flakes over top, if desired.