Using a small skillet over medium heat, add the fennel seeds and cook until fragrant. About 2 minutes. Don't let them burn.
Using a motar and pestle, ground until coarsley crushed. If you don't have a mortar and pestle, you can try using a cutting board and can. I decided to use my spice grinder and crush them to a powder.
Once toasted, add to a large bowl, big enough to add all the chicken pieces. Add the orange juice, orange zest, minced garlic, allspice, red pepper flakes and honey.
Season the chicken with salt and pepper and add to the bowl. Using a spatula, turn the chicken pieces to coat them with the marinade.
Add the plum slices and thyme sprigs. Give the chicken a quick stir, cover and refrigerate for at least 2 hours up to 24 hours.
Preheat the oven to 425°F when you are ready to start cooking.
In a rimmed sheet pan (or roasting pan) coated with spray oil or olive oil, add the chicken pieces. In between the chicken, add the plums, onions and potatoes.
If there is any liquid left in the bowl, spoon it out evenly over the chicken.
Drizzle a little olive oil or spray with canned olive oil. Season with salt and pepper.
Place in the preheated oven and roast for 45 minutes or until the chicken thighs are done.
To serve, plate the chicken pieces, spoon the plums and onions around the chicken and add the potatoes.
There most likely is going to be some pan juices in the pan. Spoon or drizzle the juices over the chicken.
Garnish with shredded basil and serve.