Place chicken breasts in between plastic wrap and pound until ⅓ inch thick.
Heat 1.5 tablespoon of olive oil in a large pan.
While olive oil is heating, season chicken with salt and pepper on both sides.
Sear the chicken 5-6 minutes on each side, over medium high heat until outside is browned. You’ll have to cook the chicken in 2 separate batches depending on the size of your pan.
When chicken is cooked, set aside on a plate.
Add remaining 1.5 tablespoons olive oil into the pan.
Saute garlic, onion, red pepper flakes and rosemary for 5 minutes, uncovered over medium heat, until translucent.
Once translucent, add red wine and cook for another 5 minutes, uncovered.
Add crushed tomatoes and bring to simmer.
Once simmering, add cooked chicken back to the pot. Cover and cook for 1-2 hours on low, stirring every 30 minutes. The chicken will begin to fall apart.
When ready to eat, gently break apart the chicken. Serve over zucchini noodles or pasta.