Gather all ingredients and heat grill to 425 degrees.
Lay your flank steak onto a cutting board and start slicing it in half.
Keep cutting, try to stay in the middle of the steak so both sides are the same width. Cut until about one inch left on one side.
Open the steak up like a book.
Add your chopped spinach to a bowl, pour in your bread crumbs.
Add in roasted red peppers.
add in egg yolk.
add in blue cheese.
add in garlic salt.
add in black pepper.
mix everything together.
season steak with salt and pepper.
Start spreading your mixture onto the steak.
spread everything evenly onto the steak, leave about 3/4 inch on all sides.
start rolling your steak up really tightly.
roll all the way up and grab your butchers twine.
Tie one end of the stuffed steak up.
start tying the steak up all the way to the other end leaving about a 1 1/2 inch gap between the knots.
Pour olive oil on to the outside of the steak. Try to coat the whole outside.
Season the outside with salt and pepper.
Place steak directly onto the grill.
After 10 minutes, roll the steak to grill the other side.
Keep rolling the steak around to make sure the outside is cooking evenly.
Remove from the heat, and allow to rest. Cut the steak in-between the ties and serve!