mojolicious_app.pl

use base 'Mojolicious';

__PACKAGE__->attr(
    'config' => sub {
        {   foo => 'bar',
            bar => 'foo'
        };
    }
);

sub startup {
 my $self = shift;
 $self->config->{baz} = 'bzzzzz';
# code
}

@@ index.html.ep

<%= app->config->{baz} %>