Tomato sauce in USA/Canada can be replaced with tomato puree or passata in other countries.
Spice level: It has a little kick, so you can up the cayenne pepper if you want more heat or eliminate it if you want it mild (but ensure the curry powder you’re using is mild if that’s a concern).
You can swap the chicken breasts with boneless skinless chicken thighs if desired. They’re less likely to dry out.
If you’re not using sea salt or kosher salt, you may want to start with half the suggested salt amount.