Return lasts post with featured image in php

Hi! I am trying to write a shortcode, that returns the lasts posts, with the fetaured image.

So far I do have this:

$output = '';

	$args = array(
	'posts_per_page' => 3,
	'meta_key' => '_thumbnail_id'
	);
	$recent_posts = wp_get_recent_posts( $args );
	foreach( $recent_posts as $recent ){
		$output .= '<li><a href="' . get_permalink($recent["ID"]) . '">' .   $recent["post_title"].'</a> </li> ';
	}

	return $output;

But I am not sure how to use the 'meta_key' => '_thumbnail_id' for <img src="featured.png">.

Any idea how to solve that? ?? Thank you!