"ארוחת בוקר מצוינת."
Translation:An excellent breakfast.
Yes, it's not simple. You would need a copula here to turn this into a sentence "Breakfast is excellant". But you are right to observe that you don't always need a copula. The case in which you don't need a copula is when you want to say that the "noun" is "adjective" but the subject is definite.
ארוחת הבוקר מצויינת.
The reason that you don't need a copula in this case, is that it is not ambiguous, it can't mean "the excellent breakfast" because that would require an article on the adjective as well: ארוחת הבוקר המצויינת.