the use of "the"

Hello, I am lost on the use of definite article "the"--when is it used, and not used, in Spanish. Two examples are given below. The first I know for a fact that the definite article is used: 1) Estaba cocinando _el_ desayuno But in the second example I have heard and have used: 2)...en vez de papas quisiera... Why is it not "...en vez de _las_ papas..."? Or can be used with or without? What is the rule? Thanks.

I asked a friend from mexico you question, and here is her answer: . In the example you mention about "las papas" I would use both indistinctively. *__en vez de papas quisiera__... means instead of fries I want/or I would like.....* *__en vez de las papas__. means instead of the fries. that are incuded in this meal (implicit)*