Cook the spaghetti according to package directions, drain and keep warm.
Heat the olive oil and butter together in a sauce pan. Saute the garlic and onions until fragrant. Add the chopped tomatoes and cook for about two minutes or until they start to soften. Add all the contents of the jar, removing the bay leaf, if any. Cook for a few minutes, stirring to break up the sardines. Try not to turn the sardines mushy with over mixing; it’s nice to eat the pasta with discernible bits of sardines.
Season the sauce with salt and pepper. Add the cooked pasta to the sauce and toss to coat evenly.
To serve, place the cooked pasta in individual plates, top with chopped cilantro and grated cheese.