Bring water to a boil, salt it and cook pasta to al dente.
In a mixing bowl, whisk together the orange marmalade, garlic, oregano, mustard and vinegar. Stream the olive oil into dressing while whisking and season dressing with salt and pepper. Pull off 8 of the outer leaves of radicchio. Form serving cups for the pasta salad out of the leaves using 2 leaves to form each bowl. Chop remaining radicchio. Toss radicchio and pasta and onions with the dressing to combine. Serve pasta in lettuce bowls.