Bring a large pot of salted water to a boil. Cook the rigatoni according to package directions until al dente. Reserve ½ cup of pasta water, then drain and set aside.

In a large skillet over medium heat, cook the bacon until crispy, about 8 to 10 minutes. Remove with a slotted spoon and set aside, leaving about 2 tablespoons of bacon fat in the pan.

Add the diced onion to the skillet and cook for 2 to 3 minutes, stirring often, until softened.

Add the mushrooms and season with salt and pepper. Cook for 5 to 6 minutes, stirring occasionally, until they release their liquid and begin to brown.

Return the cooked bacon to the skillet. Add the heavy cream, chicken broth, and Dijon mustard. Stir to combine and bring to a gentle simmer over medium heat. Cook for 3 to 5 minutes, stirring occasionally, until the sauce slightly thickens and coats the back of a spoon.

Turn off the heat and stir in the Parmesan cheese and lemon juice until smooth and creamy. If the sauce is too thick, add a splash of reserved pasta water to loosen.

Add the cooked rigatoni and toss until evenly coated in the sauce.

Serve immediately in warm bowls and garnish with fresh parsley.