chopping onions, bottle caps

Question

Hi Rabbi, I noted that you give pask on this site, not a machloket, so i would like to know the actual din lemaaseh [1] may one chop onions dak dak right before a shabbat meal for use or is this tochen ? other veggies? [2] may one open soda bottle, grape juice bottles and thereby break either plastic or metal rings ? thank YOU