Translation:We are talking about the Universe during the lesson.
My Polish wife says that in this case lekcja takes the same form in singular as in plural, which would mean that '...in lessons' should be accepted as well.
I think it's treated kind of like a geography word, also we do only know one Universe, so that make sense to capitalize it... to me, at least.
It seems that this small typo (missing L in 'talking') made the program reject your answer. We don't control what is accepted 'with a typo' and what is rejected.
Could the "our" be implied here, as in "We are talking about the Universe in our lesson" since the subject is "we"?
It seems possible, I guess... added.
Would the students actually talk about 'our lesson', though? 'Cause the contexts in which I imagine this being said are rather rare, but maybe I'm just not aware that it's more common.
No, lectures (wykłady) are rather at university and lessons (at least Polish "lekcje") at school.
Why do you suggest The Present Continuous Tense? They may talk about the Universe every day. So, I prepare using in the sentence: We TALK... during a lecture