Meta tags in shortcode

Since evasmat_posted_on() is a function in your theme, you don’t need to use get_post_meta to get the date. You can call the function directly so:

function evasmat_posts_shortcode(){
    $q = new WP_Query(
        array( 'orderby' => 'date', 'posts_per_page' => '4')
    );

    $list="<div class="cards">";

    while($q->have_posts()) : $q->the_post();

        $list .= '<div class="card">' .  get_the_post_thumbnail() . '<h2 class="entry-title-index"><a href="'.get_permalink().'">'.get_the_title() .'</a></h2>'  .'<div class="entry-meta">' . evasmat_posted_on() .'</div></div>';


    endwhile;

    wp_reset_query();

    return $list . '</div>';

}

add_shortcode('recent-posts', 'evasmat_posts_shortcode');