Thank you all for your quick and helpful responses! Wow, this really works! I ended up adding a bit of cayenne to the yogurt. Mujaddara smells sooo good and Potluck is at noon!

I've never made Rivka's exact recipe, but it's very similar to a classic Middle Eastern one I make quite often (from Paula Wolfert's recipe.) I agree both Aleppo and Hot Paprika are great to have on hand, but I really wouldn't worry about using the precise one this time - just use some cayenne or whatever is handy.

This is the kind of traditional dish that every home cook makes slightly differently anyway: the proportion of onion, type of rice, blend of spices...personally, I sometimes do the yogurt with lots of spices, etc.; other times, depending on what I'm serving with it, very simply with just, e.g.,garlic, lemon, spicy paprika and s/p. It's a very forgiving dish, open to personal interpretation.

Not surprised you're having trouble finding the Aleppo, but spicy pap is usually easy (around here, anyway.) For future use, Szeged is the brand I usually see, even in my supermarket. The can looks like this: http://www.amazon.com/Szeged-Paprika-HOT-szeged-5oz/dp/B000LRG0W4
(Hungarian, not Mid Eastern, but works perfectly fine.)

worth getting some Aleppo pepper. a bit of heat, but not too much, and great flavour. I use it all the time in all kinds of things. Become a real staple for me!

You could also use a pinch or two of cayenne and a pinch of paprika. You might have to mail order the Aleppo pepper for future. Penzey's carries it as do Middle Eastern markets.

It is the BEST! I've been making it every week--had leftovers for lunch today. You could leave out the aleppo pepper, but if you want some heat, some red pepper flakes will be a good substitute.

Maybe the paprika you bought, plus a little cumin and chili powder.