"Would you like a bento?"
Literally translated, the sentence reads "Regarding a bento, how about it?" いかが Isn't a verb, just like ほしい and 好き aren't verbs (although Duo teaches them as if they were). ほしいです means "it is desired" and 好きです means "it is liked." The verb in this sentence is the "is" (です) at the end.
These discussions are important, as the difference between idly wondering if someone wants a thing, and offering to provide it, are quite major.
I wonder if, in japanese, you can do that joke that works in English ...
A (wanting B to bring tea for the guests ) "how about some tea?" B (misunderstanding as an offer ) "lovely, white with two sugars please ".