Bring a large pot of salted water to a boil. Cook the rotini pasta according to package directions until al dente.
Drain the pasta and rinse briefly under cool water to stop the cooking process. Drain well.
Transfer the cooled pasta to a large mixing bowl. Toss with 1 tablespoon olive oil to prevent sticking.
Add the orange bell pepper, cherry tomatoes, sliced black olives, purple cabbage, mozzarella pearls, Italian dressing, Italian seasoning, and black pepper.
Toss gently until the pasta and vegetables are evenly coated. Taste and add salt if needed.
Cover the bowl and refrigerate for at least 30 minutes.
While the pasta salad chills, wash and dry the English cucumber. Slice it into 1/4-inch rounds.
Use a small paring knife to carefully carve two triangle eyes, a small triangle nose, and a curved or zigzag mouth into each cucumber round to create Jack-O’-Lantern faces.
If desired, brush the cucumber slices lightly with lemon juice. Place them on a paper towel-lined plate, cover, and refrigerate until serving.
Before serving, stir the pasta salad. Add an extra splash of Italian dressing if needed.
Transfer the pasta salad to a serving bowl or platter. Arrange the Jack-O’-Lantern cucumber slices on top, face-up.
Serve immediately, or keep chilled until ready to serve.