Preheat the oven at 180 °C.

Reserve 9 slices of pepperoni, a bit of bell pepper, and some onion for later.

Whisk the egg in a bowl. Add in the ricotta, parmesan, and 1 cup of mozzarella.

Take another bowl and mix the rest of the pepperoni with the pizza sauce, water, the rest of the bell pepper, and the rest of the onion.

Boil some water and submerge the lasagna sheets for 2 minutes to soften them. The pasta shouldn’t be completely cooked, just soft.

Spread ½ cup of the pizza sauce at the bottom of a casserole and cover it all with lasagna sheets.

Begin with the layers: a layer of the cheese mix, then a layer of pizza sauce, then a layer of ground beef, and then another layer of sheets. Repeat all the layers twice; the last layer should be lasagna sheets.

Spread what's left of pizza sauce on top, sprinkle the rest of the mozzarella, and also the pepperoni, bell pepper, and onion reserved before.

Bake for 45 minutes and then let it rest for 10 minutes.