I had the same problems as you, until I found a recipe online which I adapted to be SW friendly, and the key to it I think is that it uses pureed onions and pureed lentils.
It goes a bit like this: (roughly!)
mix together...
1 tsp chilli powder
1 tsp garlic paste
1 tsp ginger paste
1 tsp turmeric
1 tbsp curry powder
a little water
This will make a paste.
Chop up an onion or two, and fry them in frylight for a bit.
Bung in some chicken or quorn and fry that too.
Then add in your curry paste that you've made. Stir it up.
Chuck in any other veggies you like, peppers, mushrooms, etc.
Let it fry for a little while, you might need to add a bit more water if it sticks.
Next mix together about 1/2 a pint of chicken stock (oxo cube), a couple of tbsp of vlf yog, (make sure its not too cold or it'll curdle) 2 tsp tomato puree, and your onion and lentil puree (you literally chop up some onion, as much as you want (i do 2/3 little ones), fry them a bit, add a bit of water, then blitz with a hand blender. Same for lentils, boil them a bit then whizz them up)
Mix this all together, then stir it into your curry on the hob. Again, you could add a bit more water if its too thick.
Let it simmer away on a low heat for a while, then you're supposed to stir in 1 tsp of garam masala at the end, but i'd run out so didn't bother. You can add some fresh pineapple at the end of this just before you serve and it makes it like a dhanzak. yum!
I've varied it a bit with more chilli powder, a bit of sweetner, and so far so good. The pureed onions and lentils give it an amazing "proper" curry texture, almost like a korma, but it tastes spicier and really really yummy!
The garlic, ginger and tomato paste are probably some syns, but i don't know how many and to be honest, this would serve 3/4 people so i think syns are negligable! Serve with brown rice and maybe some aloo gobi!
Good luck! xxx