Wash the spinach well, microwave (500 W) for 1 1/2 in plastic wrap. Wrap the frozen veggie mix in plastic wrap and microwave for a minute.
Drain and squeeze out the water from the spinach and cut into 5cm pieces. After cutting, squeeze out the water again.
In a heated pan, melt the butter. Add the spinach and mixed veggies. Quickly fry, season with salt, pepper, and soy sauce, and you're done.
Here's a batch divided into smaller servings and frozen. Add in bentos frozen and it should thaw out by lunchtime.
Story Behind this Recipe
Premade frozen vegetable can cost quite a bit, but if you make it yourself, you don't need to worry about additives and preservatives and it'll be cheaper too. Kill two birds with one stone. While this isn't a groundbreaking recipe, I couldn't find one like it when I searched, so I uploaded this.
The spinach should still be a little firm after microwaving. If you over cook the spinach, it loses its color. This just needs a brief stir fry. I cook mine less than a minute. I like it in my bento with a little soy sauce.