I started out with the recipe in Diet for a Small Planet, a book I used a lot before the internet.
Recipe is here
I‘ve strayed from this and made my own adjustments over the years, and read and tried versions I’ve seen online and had it cooked by other people. I’ve had bad versions, and fantastic versions I’ve tried and failed to recreate. Like any of these traditional ancient dishes I wouldn’t say there’s a definitve version. But that one I’ve linked to is the first one I had cooked for me, and it inspired me to buy the book and make it myself.
This looks like a good step by step guide too. More detail than the one above
Mujadara is a signature Middle Eastern dish of lentils and rice w/ crispy fried onions. Popular flavor-packed dish. Makes for a healthy feast! Vegan, GF
www.themediterraneandish.com
ETA
It may be nostalgia and association because this is the way I had it the very first time: my favourite accompaniment for this dish is just crispy cos lettuce with olive oil and lemon dressing.