Spray the inside of a 6-quart slow cooker with nonstick spray. Set aside.
In a skillet over medium-high heat, cook the pork until cooked through. Season with 1/2 teaspoon kosher salt, drain any fat, and set aside.
Using paper towels or a clean kitchen towel, squeeze the liquid out of the thawed spinach. Set aside.
In a medium bowl, stir together the ricotta cheese, parsley, and Parmesan cheese. Season with salt and pepper to taste, then add 1/2 cup of the mozzarella cheese and the spinach and mix thoroughly.
Pour 1/2 jar of the sauce in the bottom of the slow cooker. Top with 2-3 of the lasagna noodles (you will need to break them into pieces to get them to fit properly). Top the noodles with half of the ricotta cheese mixture, then half of the cooked pork, then another 1/2 jar of the sauce. Layer with 2-3 more noodles, then repeat with the rest of the ricotta, pork, and another 1/2 jar of the sauce. Top with more 2-3 more noodles (you will not have used the whole box of pasta) and the remaining sauce.
Cook on low for 4-6 hours or on high for 2-3 hours, or until the noodles are cooked and the sauce is bubbling. Turn the slow cooker to warm, top the lasagna with the remaining 1 cup of mozzarella cheese, and place the lid back on for about 15 minutes, or until cheese is melted.
Notes
Ground beef may be substituted for ground pork. Lasagna may be assembled up to a day ahead and stored in the refrigerator before cooking.