First, I thought this was a GREAT combination of my favorite Ethiopian lentils and Doro Wat (without all the butter). I didn't find it a overly spicy (in fact, I thought it could have used a little more heat like Doro Wat) and I used the entire 5 Tlbsp. This leads me to believe that berbere spice must vary in its heat level by brand. I would suggest tasting your particular brand of spice before adding it to the recipe and adjusting accordingly.
I used red onions because that's what the recipe called for and I happened to have them on hand. I'm not sure why the recipe calls for the red onions, and I'm not sure they're necessary. My lentils (I cooked my stew for 9 hours on low because that's how long I was gone) fell apart a little more than I would have liked, and that affected the texture. Green or brown lentils might have held up better, but the lentils I love at our Ethiopian recipe are also red. Maybe next time I will braise the chicken instead of cooking it in a slow cooker to see if that helps the texture of the lentils. Regardless, I WILL be making this again! Yum!