．。
1. Cut the chicken breast into thin strips.
Literal
1. chicken-breast meat [object-を] thin-cut [into-に] do.
Step 1 of a recipe, in the same terse instructional register as the lab-procedure sentence. ~にする ('make into X,' 'turn into X') attached to a descriptive noun like 細切り ('thin cut/strip') gives the 'cut into thin strips' meaning — Japanese often expresses cutting styles this way: みじん切りにする (mince), 輪切りにする (slice into rounds), 千切りにする (julienne). とりむね肉 is 'chicken breast meat' — a compound of とり ('chicken,' more casual than 鶏肉) + むね ('breast') + 肉 ('meat'). The verb is again plain dictionary form, the recipe register.