Boil a large pot of water, add a generous pinch of salt, and cook pasta to al dente, according to package directions. Drain and set aside.
While the pasta cooks, warm olive oil in a large skillet set over medium heat. Add the onion and sauté 2-3 minutes, just until softened.
Add beef and cook 4-5 minutes, crumbling it into pieces, until nicely browned.
Stir in chili powder, garlic powder, Italian seasoning, salt, and pepper, followed by the tomato sauce. Stir well and cook 3-4 minutes, until the sauce thickens slightly.
Stir in the cream until warmed through, then add drained pasta shells, toss well, and serve.