Fill a 3-quart pot with water, bring to a boil, and add a pinch of salt.
Add the gnocchi to the boiling water and cook over medium heat until they float to the surface, then use a slotted spoon to transfer them to a plate.
Heat a large skillet over medium heat and melt 1 tablespoon of the butter.
Add the cooked gnocchi to the skillet in batches and pan-fry until golden and lightly browned; remove to a plate and repeat as needed.
Add the remaining 1 tablespoon butter and the olive oil to the skillet and warm.
Add the chopped onion and sauté for 2 to 3 minutes, stirring often, until softened.
Add the minced garlic and cook until fragrant and the onion is translucent, about 30–60 seconds.
Add the dried oregano and Italian seasoning and cook, stirring, for about 1 minute to bloom the herbs.
Pour in the crushed tomatoes, stir to combine, and simmer the sauce for about 5 minutes.
Add the pan-fried gnocchi to the sauce, toss to coat, and season with salt and black pepper to taste.
Serve the gnocchi topped with shredded mozzarella, grated Parmesan, and sprinkle with crushed red pepper flakes.