Calculating user efficiency on a time period with Linq
Don't one line things that shouldn't be one lined. Just because you can do something, doesn't mean that you should. 
Extract the duplicated query into a method of it's own that returns an IQueryable
Don't query the database twice for the same count, execute the query and store it in a variable.

private IQueryable&lt;foo&gt; ExecutorOrdersInLast30Days(ApplicationUser e)
{
    return e.ExecutorOrders.Where(x =&gt; x.Added &gt;= DbFunctions.AddDays(SqlFunctions.GetUtcDate(), -30));
}

private decimal EfficiencyPercent(ApplicationUser e)
{
    var nonDeletedOrders = ExecutorOrdersInLast30Days(e).Count(x =&gt; x.Status != Order.OrderStatus.Deleted);
    if ( nonDeletedOrders &gt; 0)
    {
        return nonDeletedOrders / ExecutorOrdersInLast30Days(e).Count();
    }
    else
    {
        return 0;
    }
}