It's quite hard to translate exactly, in my opinion. It's a full, sit-down breakfast. The expression was coined by the Catalan writer, Josep Pla, describing the copious breakfasts served at the Fonda Europa in Granollers. It generally consists of different calorific dishes such as pigs' trotters, pigs' ears, beans, chick peas...washed down with beer or wine, etc. It is a meal that requires a fork (and perhaps a knife) as the name suggests. So, I would perhaps say something like 'full Catalan breakfast' or 'sit-down Catalan breakfast' - or maybe leave out the 'Catalan' part. Hope that helps!

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Note added at 1 hr (2017-06-07 11:29:41 GMT)
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I agree with the previous answer too - cooked breakfast is perhaps another way of putting it, although not all elements of the meal need to be cooked. As far as I know, the emphasis is really on the fact that it is a BIG meal that you sit down and take your time eating. Traditional slow food, in other words - not just a quick sandwich eaten on the way to work.