functions.php

<?php

/**
 * Mobile Menu
 *
 */
function be_mobile_menu() {
	echo '<div class="mobile-menu mobile-show"><i class="fa fa-bars"></i><i class="fa fa-close hidden"></i></div>';
}
add_action( 'genesis_header', 'be_mobile_menu', 12 );

global.js

	// Mobile Menu	
	// -- Mobile Menu Open
	$('.mobile-menu .fa-bars, .mobile-menu .fa-close').click(function(e){
		$('.site-header').toggleClass('menu-active');
		$('.mobile-menu .fa-bars, .mobile-menu .fa-close').toggleClass('hidden');
		$('.nav-header').slideToggle();
		e.preventDefault();
	})
	
	// -- Mobile Submenu Open
	$('.site-header .nav-header .menu-item-has-children > a').click(function(e){
		$(this).siblings().addClass('active');
		$('.site-header .nav-header').animate({
			left: '-100%',
		}, 500, function(){});
		e.preventDefault();
	});
	
	// -- Mobile Submenu Close
	$('.site-header .nav-header .sub-menu').prepend( '<li class="menu-item back"><a href="#">Back</a></li>' );
	$('.site-header .nav-header .sub-menu .back > a').click(function(e){
		$('.site-header .nav-header').animate({
			left: '0',
		}, 500, function(){
			$('.site-header .nav-header .sub-menu.active').removeClass('active');
		});		
		e.preventDefault();
	});		

style.css

@media only screen and (max-width: 767px) {
	/* Mobile Menu */
	
	.site-header .wrap {
		position: relative;
		padding: 0;
	}
	
	.site-header .mobile-menu {
		position: absolute;
		top: 7px;
		right: 20px;
		font-size: 30px;
		line-height: 1;
	}
	
	.site-header .mobile-menu i {
		cursor: pointer;
	}
	
	.site-header .mobile-menu i:hover {
		color: #1894a7;
	}
	
	.site-header .mobile-menu .hidden {
		display: none;
	}
	
	.site-header .nav-header {
		background: #fff;
		position: absolute;
		z-index: 10;
		width: 100%;
		display: none;
	}
	
	.site-header .nav-header .genesis-nav-menu li {
		display: block;
		font-size: 24px;
	}
	
	.genesis-nav-menu .signup, .genesis-nav-menu .login {
		margin: 10px auto;
		max-width: 300px;
		
	}
	
	.genesis-nav-menu .menu-item-has-children > a:after {
		content: '';
		display: inline-block;
		margin-left: 10px;
		width: 0;
		height: 0;
		border-style: solid;
		border-width: 6px 0 6px 6px;
		border-color: transparent transparent transparent #1894a7;	
	}	

	.genesis-nav-menu .menu-item,
	.genesis-nav-menu .menu-item:hover {
		position: static;
	}

	.genesis-nav-menu .sub-menu {
		background: #fff;
		top: 0;
		position: absolute;
		left: auto;
		opacity: 1;
		width: 100%;
		z-index: 9;
		display: none;
	}
	
	.genesis-nav-menu .sub-menu a {
		background: #fff;
		color: #2d2d2d;
		width: 100%;
	}
	
	.genesis-nav-menu .sub-menu li:hover > a {
		background: #fff;
		color: #1894a7;
	}
	 
	.genesis-nav-menu .sub-menu.active {
		display: block;
		right: -100%;
	}
	 
	.genesis-nav-menu .sub-menu .back > a:before {
		content: '';
		display: inline-block;
		margin-right: 10px;
		width: 0;
		height: 0;
		border-style: solid;
		border-width: 6px 6px 6px 0;
		border-color: transparent #1894a7 transparent transparent;
	}
}