To make the marinade: In a blender or food processor combine banana peppers, mustard, and honey. Blend until smooth, and set aside 3 tablespoons for the pasta sauce.
Pour the remaining marinade into a re-sealable plastic bag. Season the pork with salt and pepper and add them to the bag. Seal and distribute the marinade equally on the pork. Marinate at room temperature up to 2 hours or in the refrigerator if longer than that. Remove the pork from the refrigerator 30 minutes before cooking to let pork come to room temperature.
Preheat a seasoned cast iron grill pan over medium-high heat.
Bring a large pot of well-salted water to a boil for the pasta.
Remove the pork medallions from the marinade and give a gentle shake to remove excess marinade. Place on the grill pan. Let cook 4 minutes per side or until cooked through. Remove from the pan and loosely tent with aluminum foil while the meat rests.
Meanwhile, cook the pasta in salted boiling water until al dente, about 12 minutes. In a medium saute pan on medium heat, heat the oil. When it begins to swirl, add the onions. Season the onions with salt and pepper, and sweat until tender.
Add the garlic and cook another minute. Add reserved marinade and stir. Once combined, add the heavy cream and stir until slightly reduced and thickened, about 8 minutes.
Stir in the grated Parmesan, and parsley. Drain the pasta and add to sauce, coating well. Serve alongside pork.