Place the cubed baguette on a sheet tray and bake 10 minutes to dry out. Reserve.
Add the potatoes to a pot of simmering water and simmer until you just take the bite off, 10 minutes (we will cook these again in the skillet). Remove and reserve.
Turn up the oven temperature to 425 degrees F.
Heat a 14-inch heavy-bottomed skillet on high and coat with canola oil. Sprinkle the chicken thighs with salt and pepper. Sear the chicken skin-side down, working in batches if needed, until golden brown, 4 to 5 minutes. Flip and cook another 2 minutes. Remove the chicken from the skillet, reserving all of the fat in the pan.
Add the onions, sprinkle with salt and sweat until translucent and softened, 1 to 2 minutes. Add the garlic and cook 1 minute. Add the baguette cubes, reserved potatoes and carrots, and sprinkle with salt and pepper. Add the lemon wedges and lemon thyme. Toss all the ingredients in the fat with an additional glug of oil if needed. Arrange the thighs on top and place in the oven until the thighs reach 160 degrees F, about 15 minutes.