Preheat your oven to 350 degrees F. Liberally spray a 9x13 baking dish with cooking spray.
Begin cooking pasta. Cook ground beef, onion and green pepper in a skillet over medium high heat, crumbling beef as it cooks with a wooden spoon until browned. Drain off grease. Add spaghetti sauce and stir well to combine. Cover and simmer for 15 minutes, stirring occasionally.
Evenly spread 1/2 of the cooked ziti in bottom of baking dish. Evenly place slices of provolone cheese over ziti. Spread sour cream over provolone cheese. Spread 1/2 of sauce over provolone cheese. Layer remaining ziti, mozzarella cheese and remaining sauce mixture. Evenly sprinkle with Parmesan cheese.
Cover and bake for 20 minutes. Remove from oven and uncover. Return to oven and bake for an additional 10 minutes, or until cheese is melted and bubbling around edges.
Sprinkle with chopped fresh parsley, if desired.