Try red bell pepper instead of tomatoes. Too, there are lots of good white chili and white lasagna recipes online.
Also, someone told me just the other day that a slow cooker and a crock pot are not synonymous. I don't know because I've never used either one but I'm hoping I get one as a gift this year for Christmas. So I'm not sure if substitutions would make a difference in recipes that are for a crock pot if you use a slow cooker instead.