In a saucepan over medium heat, heat the olive oil, then add the yellow onions. Sauté the onions, stirring often, until cooked through (translucent, approximately 4 to 5 minutes), then add the garlic. Cook for 1 more minute, stirring often until the garlic is fragrant.
Add the crushed tomatoes and Sriracha sauce - stir to combine, then turn the heat to high and bring the sauce to a boil.
Once boiling, turn heat again to medium and allow the sauce to simmer for 10 to 12 minutes or until the sauce has thickened to your desired consistency. Add salt and pepper to taste.
Use immediately over spaghetti or the pasta of your choice.