Translation:This ramen is really tasty.
"This ramen really is delicious" would be a preferable order, being more euphonious and better highlighting " ほんとうに" as conveying a sense that the statement is one of fact rather than operating as just another intensifier like "very" for the predicate adjective. If you really meant the ramen are very tasty 「とても」would perhaps be better.
Spaghetti is plural in Italian but singular in English, and ramen is also singular in English. Noodles would be plural in English so some people might say "These ramen noodles are really delicious".
If you said "These ramens are really delicious" to an English speaker they would think you are talking about two bowls of ramen or two different kinds of ramen.
Don't worry it only sounds weird because English isn't your native language and your English Sprachgefühl is not yet at a level for it to sound perfectly fine like it does to English speakers.
According to jisho, ほんとう literally means truth, reality. Honesty is related to truth, but it is not the same. It means telling the truth, rather than simply being true. Idk whether or not "this ramen is honestly delicious" is a proper translation or whether or not "This ramen is truly delicious" is a proper translation
本当 is a na-adjective (a noun that can act like an adjective) and conjugates into its adverb form by dropping な and adding に
本当 - Truth/reality (Noun)
本当な (X) - True/Real (X) (Adj)
本当に - Truly/Really (Adv)
I tend to think of it somewhat like the location marker in these situations. Like "In truth-" Similarly しずか - Silent, しずかなこうえん - Silent park しずかに行きます - I go silently / 'I go in silence'
There's an error in this case, because it doesn't accept "tasty", which is used more often in English than "delicious".
It should accept both, but "delicious" is actually used more often than "tasty": https://books.google.com/ngrams/graph?content=tasty%2Cdelicious&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Ctasty%3B%2Cc0%3B.t1%3B%2Cdelicious%3B%2Cc0