In a large skillet set over medium-low heat, add the oil. Once the oil is hot, add the onions and garlic with a big pinch of salt. Cook the mixture, stirring occasionally, until the onions are translucent, 3 to 5 minutes.
Stir in the tomato paste and increase the heat to medium-high. Cook the tomato paste, stirring constantly for 1 minute.
Add the ground beef and cook it, breaking it apart with a spatula, until it is no longer pink, 5 to 7 minutes.
Stir in the prepared sauce and cook, stirring occasionally, until the sauce has thickened slightly, about 3 minutes. Taste and season the mixture with salt and pepper.
Spoon the meat mixture onto buns and serve.