Hi, I make a lot of curries and always use the following....
I frylight onions, garlic, chilli and ginger (if I have it) in 2tbsp garam masala, 1/2 tsp cumin, 1/2 tsp turmeric. Once softened add a tin of tomatoes and a tsp sweetner (if reqd) and simmer. This makes a great base for any meat or veg curry and if you like it smooth then you can whizz it up once cooked.
It's also lovely with some FF natural yoghurt stirred in at the end.
Also.... if you use a slow cooker, do the onions in the spices in the pan and then chuck everything in the slow cooker.