In a small bowl combine, salt, ground coriander, lemon zest, ginger, pepper and garlic.
Pat the chicken dry. Rub the spice mix all over the chicken. Put some under the skin and in the cavity. Stuff the thyme sprigs into the cavity.
Put the chicken onto a baking pan. Let it sit uncovered in the refrigerator for at least 1 hour or overnight to let the spices seep in.
30 minutes – 1 hour before you’re ready to cook the chicken prepare the rhubarb: In a 9″ pie pan or baking dish, toss together the rhubarb, ginger, coriander, lemon juice, lemon zest, and thyme sprigs. Add honey and mix to combine. Let rhubarb macerate at room temperature for 30-60 minutes.
Preheat oven to 425 degrees. Toss the red onions in a medium mixing bowl with a drizzle of olive oil and a pinch of Celtic sea salt and set aside.
Drizzle olive oil all over the chicken. Roast the chicken in the center rack of the oven and rhubarb below for 20-25 minutes until the rhubarb is tender.
Remove the rhubarb and stir to break it up. Spoon some of the rhubarb and it’s juices all over the chicken.
Reduce the temperature to 400 degrees. Scatter the red onions around the chicken on the baking pan.
Return to the oven and roast until the skin is golden and the chicken is cooked through, about 20 minutes longer. An instant read thermometer stuck into the thigh but not touching bone should read 165 degrees Fahrenheit.
Let chicken rest 10 minutes. Carve and serve with onions and rhubarb sauce on the side.