The question what you want. The .where statement needs a predicate. For example you can use something like this:
context.table1.Include("table2").where(a => a.value = 10));
or
context.table1.Include("table2").SelectMany(a => a.Table2.Where(b => b.value = 20));
or
context.table1.Include("table2").SelectMany(a => a.Table2.Where(b => b.value = 20), (a,b) => new { item1 = a, item2 = b } );