Make the multi-seed oat mixture: in a small bowl combine the rolled oats and all the seeds. If you can't find each variety of seeds, it's ok. I think the two most important texturally are the sunflower seeds and the rolled oats. The poppy seeds come into play in the appearance department but if you just have those three seeds/oats you will be ok.

Once they are all combined, place them in a sealed container in a cool spot in your kitchen and they will last for a few months at least (probably a lot more).

Sandwich loaf: weigh and add all of the sandwich loaf ingredients to a large bowl or the bowl of your stand mixer. If you are kneading with a mixer, mix on medium speed for 8 minutes. If you are kneading by hand, you will need to knead it for around 15 minutes to get a smooth dough. 

Add dough to a lightly oiled bowl and place it in a warm spot in your kitchen. Allow to rise for 1 to 1.5 hours.

After an hour or an hour and a half, place your dough on a lightly floured surface and deflate all the bubbles/gas. Shape the dough into a rough rectangle about the length of your 4x8-inch pan. 

Lightly grease your pan with olive oil or non-stick cooking spray.

Roll the dough rectangle up fairly tightly into a rough cylinder about 8 to 9 inches long. Pinch the seam tight and roll the cylinder a couple of times to smooth it out a little. Place the cylinder seam side down in the pan. Press it around with your fingers a little to make sure it fits properly into the corners. 

Cover the pan/dough with a lightly greased piece of plastic wrap. 

Allow the dough to rise in a warm spot for 45 to 60 minutes until the dough has risen about an inch above the top of the pan. 

Near the end of the final rise time, preheat oven to 350 degrees F (190 C). 

Topping: crack a whole egg in a bowl with 1 tablespoon of water and whisk to combine thoroughly. With a brush or a spoon, carefully paint the egg wash on top of the risen loaf inside of the loaf pan. Once the whole loaf has been painted with egg wash, sprinkle 2 to 3 tablespoons of seeds/oats on top of the loaf. Try for an even sprinkled coverage. The egg wash will help with browning the loaf but it will also help the seeds to stay adhered to the top of the loaf.

Bake bread for 30 to 35 minutes and remove from pan to a cooling rack to fully cool before slicing. The bread should be 190 degrees F internal temperature. 

Do not slice for at least an hour because the bread is technically still cooking. 

Slice and sandwich.