Jack cheese is added along with the half-and-half to temper the mixture and prevent curdling. Use only a top-quality chardonnay or other wine you'd want to drink; it will make a big difference in the sauce.
Heat the oil in a Dutch oven over medium-high heat. Add bell pepper, onions, and garlic; sauté 5 minutes. Add wine and mussels; cover and cook for 5 minutes or until mussels open. Discard any unopened shells. Remove mussels from pan with a slotted spoon; cool. Remove meat from mussels; set aside. Discard shells.
Add the cheese, half-and-half, salt, and black pepper to pan; reduce heat, and cook 5 minutes or until cheese melts. Stir in mussels, and cook for 4 minutes or until thoroughly heated. Combine the mussel mixture, spinach, and pasta, tossing well.