Could you be awkward and do that? Yes. Would someone trying to assimilate the information probably give up on having a conversation with you because you're speaking in tongues? Yes as well.
If you want to be understood, you need to keep blocks of things that go together (your S, your V and your O), regardless of the word order inside and outside the blocks.
In Esperanto "mal" does not mean bad, It gives the opposite of the following word. "Bon" is good, so "malbon" is bad, so the second is the correct one. "malbongusta" would mean "bad tasting" which is the opposite of delicious. Another example, "rapide" is "fast" and "malrapide" is slow. http://www.gutenberg.org/files/16967/16967-h/16967-h.htm
Careful with one letter difference: "malĝusta" means "incorrect" or "wrong".
Also, "sengusta" is "tasteless".
"Delicious" and "tasty" are listed as synonyms for each other. http://www.merriam-webster.com/dictionary/delicious http://www.merriam-webster.com/dictionary/tasty
On the other hand "bongusta" is listed as "good taste" and supporting you, "bongustega" is listed as "delicious". http://esperanto-panorama.net/vortaro/eoen.htm Perhaps we should report this.
English can put one noun before another one to modify it like an adjective -- much as you can have a "big book" you can also have a "physics book", where the noun "physics" modifies "book" like an adjective.
Esperanto doesn't do that.
So if you want to say "chocolate cake", for example, you have to turn the noun "chocolate" into an adjective explicitly -- from ĉokolado into ĉokolada. Then there can be a ĉokolada kuko "chocolate cake". And if you have one, you have ĉokoladan kukon "chocolate cake" (with the accusative ending -n).
If you said ĉokolado kuko with just two nouns next to each other, it sound a bit as if you said "size book" instead of "big book" -- you just can't put those two nouns together like that and expect it to make much sense.
Given that I found myself wondering, while doubting that anyone else was wondering if the She of this sentence had a singular mass of chocolate (apparently she does) versus a single piece of chocolate, I still came here to try to find out the following:
Would there be a different ending for ĉokolad- in the latter context (since Esperanto doesn't indicate the singular, just the lack of plural). other than 'unua ĉokoladon' or 'unua fragmenton de ĉokoladon'?
Because it's an adjective.
ĉokolado is a noun, so it ends in -o.
bongusta is an adjective, so it ends in -a. The adjective bongusta describes the noun ĉokolado. What kind of chocolate is it? Delicious chocolate.
And since the bongusta ĉokolado is the direct object of the verb havas, it gets put into the accusative case, and both the adjective and the noun get the accusative case ending -n -- bongustan ĉokoladon.