This is a simple tomato sauce I use with my braciole.
1/4 cup olive oil
1 large white onions, diced small
1 Tbsp Italian Seasoning
2 Tbsp dried Oregano
1 Tsp red pepper flakes (bump up to 2 tsp to make fra diavolo)
4 garlic cloves - minced
Salt and Pepper to taste
2 cans diced tomatoes (400g // 14.5 oz). I prefer the Cento brand small diced or Tesco Italian Finely Chopped Tomatoes (if in the UK)
In a medium sauce pan, heat oil over medium/medium high heat
Add onions and saute till translucent
Add spices and salt and pepper, stir to combine
Add garlic, saute for 1 min...don't let it burn
Add tomatoes
Bring to a simmer and reduce heat to low.
Let simmer for approx 30 min.