"Rice" is a non-count noun, meaning you can't use it with an indefinite article (a/an) and there is no plural form. I would also find it more normal to say I had "curry" for lunch - or "curry with rice", although I also always just assume a curry is served with rice? "Curry" can be a countable or non-count noun ("I had curry for lunch" or "I had a curry for lunch").