I do a similar mixture to shrimpy. I tend to use fresh chilli's where possible though instead of chilli powder, as I find you just don't get the same flavouring from chilli powder.
Also if you want it a bit more spicy (I do) add a bit of cayenne pepper. But you only need a tiny bit, don't go mad. I normally add about 1/4 of a teaspoon at a time, taste and then add more if needed.