Center the oven rack; preheat the oven to 400°F. Put the gnocchi in a large pot of boiling salted water. Cook just until the gnocchi floats to the surface -- 2-3 minutes. Drain and set aside.
Tip the olive oil into an oven-proof skillet set over medium heat. Stir in the passata, garlic, Italian seasoning, red pepper flakes, salt, pepper, and onion powder. When the sauce begins to bubble, stir in the heavy cream. Reduce the heat to "low," and let the sauce simmer until slightly reduced -- 3-5 minutes.
Add the spinach to the sauce, and stir until the leaves wilt -- 30 seconds to 1 minute. Then stir in the sliced olives and the gnocchi. Use a spatula to break up any gnocchi that have stuck together. Off heat, taste carefully for seasonings. You might like to add more salt, pepper, or red pepper flakes.
Top the sauce with the three cheeses, starting with the Parmesan and finishing with the mozzarella.
Bake in the preheated oven until the cheese melts -- 15 to 20 minutes. Then, if desired, place the skillet about 6 inches beneath the broiler until the cheese turns spotty brown -- 45 seconds to 1 minute. Serve hot, along with a side salad and a bottle of good Cabernet!