Cook pasta shells according to package directions until al dente. Drain the shells, return them to the pot and toss with 1 teaspoon of the olive oil to prevent sticking.
Meanwhile, in a large skillet, heat the remaining 2 tablespoons of olive oil. Add the garlic and cook over moderate heat until golden, about 4 minutes. Add the peas and ham and cook until the peas are hot and the ham in lightly browned, about 5 minutes. Add the cream and stock and simmer over moderate heat until thickened slightly, about 5 minutes.
Stir the cream sauce into the shells. Add the parmesan and dill and season with salt and pepper to taste.