Here's a link from an old post re pastitsio:
Funny, now, when I look back, I see how my recipe (and cooking skills) have evolved over time.
I make it with ground lamb, (or ground beef, in a pinch), saute the ground lamb, add cinnamin, a tbl or so of tomato paste (or diced, drained tomatoes), and a handful of raisins. The sauce is a bechamel or white, and I sprinkle the top with nutmeg. It's more detailed than what I've listed here -- but the original Greek recipe always tastes the best, to me. The Greek cheese and sauce really make the dish.
If you want a 'quick' recipe, rather than make the bechamel, buy a pkg of white sauce - not the way I would do it - but it's one idea. Another is - make mac n cheese with white cheddar - again, it's not a Greek dish, albeit it is quick.
The first pastitsio I made, eons ago, was a recipe from a mag. using mayo in the sauce. A little dry, but turned out pretty well, for its' time.
Never heard of adding ground turkey or green or red peppers (noticed it's optional), so would like to know if you tried the recipe, and how you liked it. Sounds like an interesting casserole - but not ethnic, imo.