The current API does not allow this combination of criteria. There's a patch attached to DATASOLR-105 which could help though it does not solve the problem fully.
Usage of SimpleStringCriteria
might help for now. Please be aware of the fact, that values have to be converted to a Solr readable format.
new SimpleQuery(new SimpleStringCriteria("(x or y) and z"));
Update
Version 1.2
will have this issue fixed, so that its possible to create the query as follows.
Criteria orPart = Criteria.where("x").is("foo").or("y").is("bar");
Criteria andPart = Criteria.where("z").is("roo");
Query query = new SimpleQuery(orPart.and(andPart));