Learn Polish: Praca w biurze była wczoraj zbyt męcząca. - Work in the office was too tiring yesterday.

Yes, you could say za męcząca. Both zbyt and za mean "too" (as in "too much" or "excessively"), and they are usually interchangeable before an adjective. Zbyt sounds just a little bit more formal or careful, while za is extremely common in everyday, casual speech.

Why is it w biurze instead of w biuro?

When you are talking about a physical location using w (in), the noun must take the Locative case. The dictionary form is the neuter noun biuro (office). In the Locative case, the -o changes to -e, which forces the consonant r to soften into rz, giving us biurze.

Why does the word for "tiring" end in -a (męcząca)?

Adjectives in Polish must match the gender of the noun they are describing. In this sentence, męcząca describes praca (work). Since praca is a feminine noun, the adjective takes the feminine nominative ending -a.

The word order is slightly different from English. Could I put wczoraj at the end: "Praca w biurze była zbyt męcząca wczoraj"?