In a large sauté pan on medium heat, add in olive oil and sauté the salted onions for 3-4 minutes before adding in the garlic and sauté for 2 minutes.
Add in sliced mushrooms and continue to sauté for 2-3 minutes before adding in the canned crushed tomatoes. Stir in brown sugar, dried basil, and parmesan rind (if you have some on hand). Simmer for 25-30 minutes, stirring every couple of minutes.
While the tomato sauce is simmering, bring a pot to a boil and cook your gnocchi according to the package.
When ready, stir in the gnocchi and then spinach. Remove the pan from heat, add a splash of heavy cream and stir until combined. Remove the parmesan rind if you added it and top with some shaved parmesan.